Collection Care blog

53 posts categorized "Research"

20 May 2014

Discovery of a watermark on the St Cuthbert Gospel

A watermark of a post horn surrounded by a shield was recently discovered on the rear pastedown of the St Cuthbert Gospel (Add. MS 89000). The finding has just been published in the Electronic British Library Journal. The St Cuthbert Gospel is a late seventh century parchment volume and is the oldest intact European book. This Anglo-Saxon pocket gospel belonged to St Cuthbert of Lindisfarne (c. 635–687) and was discovered in 1104 in his tomb.

The pastedown, which is the endpaper attached to the inside cover board of a book, records the donation of the St Cuthbert Gospel (then known as the Stonyhurst Gospel) to the British Province of the Society of Jesus from the Reverend Thomas Philips, S. J. in 1769.

 

The front board of a book bound in dark brown leather. A rectangular decorated panel is in the middle of the board - it features a raised pattern in the shape of an interlacing vine, above and below which are rectangular panels of interlacing knot designs. The leather has deposits of dirt and small areas on the right-hand side of the board have become abraded.
St Cuthbert Gospel
A piece of cream paper pasted inside the back board of the book, covered with ten lines of Latin writing in dark brown ink. The paper is torn and folded in on the edges and at the corners. The number 91 is written in red crayon at the top of the piece of paper, above the first line of writing. The paper has some old dirt ingrained into its surface, which show the contours of the board and folds of the covering leather beneath.
Rear pastedown
A white representation of the piece of paper on the back board, showing only the outline of the watermark. The watermark is in the bottom right-hand corner. It consists of a cloud, inside which is an item in the shape of a hunting horn. A small tentacle or vine is coming out of the top of the cloud. Next to the cloud is a small design in the shape of a shoe with a high heel.
Watermark location


CC by Left: Front cover of the St Cuthbert Gospel. Centre: The rear pastedown showing a record of the donation: ‘Hunc Evangelii Codicem dono accepit ab Henrico Comite de Litchfield, et dono dedit Patribus Societatis Iesu, Collegii Anglicani, Leodii, Anno 1769; rectore eiusdem Collegii Ioanne Howard: Thomas Phillips Sac. Can. Ton.’ which translates to: ‘This Gospel Book was received as a gift from Henry, Earl of Litchfield, and given to the Fathers of the Society of Jesus, of the English College, Liège, in the year 1769, the rector of the college, John Howard, Thomas Phillips Canon of Tongres.’ Right: The watermark is located in the lower right hand corner

What are watermarks?

Watermarks are created by manipulating a piece of wire into a recognisable shape and fixing it to a paper mould such as the Japanese papermaking bamboo screen below.  Here the bamboo has been cut into strips and arranged into parallel lines called laid lines. The bamboo strips are held together by sewing thread at one inch intervals, which form the chain lines on a sheet of paper. Chain lines, laid lines and watermarks are visible when held up to a light source. Light can pass through watermarks easily because the paper thickness is reduced where wire is present in the mould.

The papermaking screen consists of two dark wood rectangular frames one on top of the other with a screen between them made from parallel strips of bamboo. A thin dark wood dowl bisects the top frame horizontally. The bamboo screen has lines of white stitching crossing it horizontally at regular intervals.
Paper mould

CC zero A Japanese papermaking bamboo screen

We typically notice watermarks on paper when they are held up to the light revealing a motif, initials or a date relating to the original paper mill. Watermarks are therefore useful in determining the provenance of paper and can help to identify its intended function. Watermarks can be difficult to image because they are often obscured by print on the page, or are located in the gutter (the space between the printed area and the binding).

An example of a partial watermark from a woodblock reprint dating to about 1476 is shown below. The reprint is of the Astronomical Calendar first published by Johann Müller (Regiomontanus) in Nuremberg in 1474 (British Library shelfmark IA.7). The watermark is found in the gutter with the other half located several folios later due to the ordering and cutting of the folios.

The gutter area of a book is shown horizontally. Grids of numbers are printed in black ink on both pages, and are coloured with yellow and red pigment on the top page. The watermark is in the margin of the top page, below the printed grid. It consists of a clover shape with three circular leaves. Two more circles like those of the leaves are positioned on each side of the central clover motif. Some of the watermark is obscured by the lower page.
Partial watermark in book gutter

CC by Watermark in the gutter of BL IA.7 when viewed through a light sheet 

When the page is adhered to a board on one side, such as the rear pastedown of the St Cuthbert Gospel, it is impossible for light to transmit and watermarks can remain undetected. A pastedown conceals the raw edges of the covering material and forms a hinge between the board and the text block.

A book bound in green leather with the front board open. The first page, the endpaper, is made from a single folded piece of cream paper, double the size of one of the book’s pages, the left hand side of which (the pastedown) is stuck to the inside of the board.
Pastedown example

CC zero An example of a front pastedown where one side of the endpaper is adhered to the front cover. Since the endpaper is fixed to the board it is difficult for light to penetrate and illuminate potential watermarks

The St Cuthbert Gospel watermark

A high resolution digital image of the pastedown was processed using ImageJ, an open source image processing software package. An image is comprised of a variety of layers or textures which can be separated. This allows pixels of interest to be isolated which may include faded writing, obscured text or watermarks. The watermark was revealed by converting the image from the standard RGB (red green blue) colour space into another space where tiny contrast differences were enhanced. The process of colour space analysis is fully explained in the publication: The Discovery of a Watermark on the St Cuthbert Gospel using Colour Space Analysis

The bottom right hand section of the rear pastedown, showing parts of the bottom six lines of writing in dark brown ink on cream paper.
No watermark observed
The same image, but with the colours reversed. The cream paper is now grey and black and the dark brown writing is shown in white. The watermark is shown in faint black lines.
Watermark visible


CC by Left: An image of the rear pastedown of the St Cuthbert Gospel where no watermark is observed. Right: The same image reveals a watermark in the lower right hand corner of the pastedown when processed into another colour space

Non-destructive science

Colour space analysis is being used at the British Library to enhance faded designs on binding covers, disclose watermarks and hidden inscriptions and to reveal text which has been chemically treated or erased. In many cases applying colour space analysis to certain multispectral images has proven successful.

Digitisation projects generate large amounts of high-resolution images which can be manipulated to discover hidden information without the need to access the item. This has significant implications for the long-term study and preservation of cultural heritage collection items. The rear pastedown in the St Cuthbert Gospel was formerly numbered f. 91 and is available to view on the internet as part of the Digitised Manuscripts website.

Christina Duffy (@DuffyChristina)

08 May 2014

Microscopy of the Lindisfarne Gospels, folio 3r

The Lindisfarne Gospels is one of the most magnificent manuscripts of the early Middle Ages. It was written and decorated at the end of the 7th century by a monk named Eadfrith who would go on to become Bishop of Lindisfarne and serve from 698 until his death in 721. An Old English gloss between the lines translates the Latin text of the Gospel and is the earliest surviving example of the Gospel text in any form of the English language. This translation was a late (mid-10th century) addition by Aldred, Provost of Chester-le-Street.

As one of the Treasures of the British Library the Lindisfarne Gospels undergoes strict condition assessments to ensure it is kept at ideal environmental conditions. Part of this assessment involves using microscopy to take a detailed look at the pigment behaviour. We posted some images in a previous post: Under the microscope with the Lindisfarne Gospels, and here we share some of the exceptional exuberance found on folio 3r.

A parchment page of illuminated text. The initial, in the upper left corner of the page, is the largest letter on the page, and extends down the left margin almost to the bottom of the page. It is decorated with swirling motifs, the heads of leopard-like animals, and interlocking birds. The main colours used for decoration are purple, light green, yellow, blue and black. There are two more letters on the first row, which are smaller than the initial but decorated in the same style. The rest of the text on the page, consisting of another five lines, is simpler and written in capitals in black ink. Some of the enclosed areas inside letters, such as A and B, are filled in with yellow, green and purple pigment. All these letters are surrounded by an outline of small red dots. A line of smaller, undecorated, red text runs along the top of each line, and an even smaller line of black text runs along the top of this
Folio 3r

CC zero Folio 3r of the Lindisfarne Gospels, Cotton MS Nero D IV. Examine in full detail here

The abstracted decoration found throughout the Lindisfarne Gospels is a spectacular example of Anglo-Saxon art. There are five major decorated openings in the manuscript, the first of which is found on ff. 2v – 3 and introduces the letter which St Jerome addressed to Pope Damasus. It was Pope Damasus who requested a revision of the Latin Bible text during the late 4th century. Folio 2v consists of an elaborate cross-carpet page and faces Jerome’s letter to Damasus in Latin with the opening Novum opus (New work). The intricate detail on this page has been interpreted as an act of personal spirituality and devotion. A few examples are shown below. Enjoy!

Top of folio 3r

A close-up of the second and third letters on the first line, showing their decoration of swirling knots and bird heads. The photo also shows the lines of red and black text running above them. There is a brown stain, caused by liquid, discolouring the parchment above the first letter.
Top of folio 3r
A close-up of two of the red letters (“p” and “I”) at 50x magnification. Under magnification the pigment appears yellow rather than red and both letters are covered with small cracks. The parchment background is grey-white and has a rough texture.
Folio 3r letter 50x
A close-up of a section of a red letter at 150x magnification. The cracks in the pigment are much larger in this photo and appear black in colour. The pigment again appears yellow rather than red.
Folio 3r 150x
A close-up of a spiral motif at 50x magnification. The spiral is drawn in black and its centre is coloured yellow. The yellow pigment is covered in cracks. There are red dots around the top and left sides of the spiral. The parchment background is grey-white and has a rough texture.
Folio 3r detail 50x

CC by Top: Upper section of folio 3r. Centre: Crackled pigment of lettering reading incipit prologus at 50x and 150x magnification. Bottom: Celtic-influenced spiral motif at 50x magnification

Centre of folio 3r

Tiny drops of red lead are also observed in early Irish manuscripts which heavily influenced the Lindisfarne Gospels. The Germanic zoomorphic style is evident with interlacing animal and bird patterns.

A close-up of the right side of the initial showing decorative animal heads which are purple with yellow noses and orange bodies. Sections of black text from the second and third rows are also shown. The black letters of the second row have areas filled in with purple and yellow pigment and are decorated with intertwining bird heads and necks. Around the initial decorative red dots are arranged in a diamond pattern; around the black letters red dots are arranged in straight lines.
Centre of folio 3r
A close-up of one of decorative animals on the initial at 20x magnification. The animal is drawn with strong black lines, and the orange pigment of its body is cracked. The parchment background is grey-white and has a rough texture.
Folio 3r 20x
The same area at 50x magnification. Cracks now show on an area of yellow pigment as well as on the orange. The purple pigment has an uneven, mottled texture.
Folio 3r pigment 50x
A close-up of the diamond pattern of red dots at 20x magnification. A single dot sits within each diamond. Under magnification the pigment appears yellow rather than red.
Folio 3r red lead 20x

 CC by Top: Central section of folio 3r from the British Library Catalogue of Illuminated Manuscripts with creature detail at 20x and 50x magnification. Bottom: Drops of red lead in a geometric pattern at 20x magnification

Bottom of folio 3r

Decorated initials exhibit yellow pigment (orpiment) bordered with drops of red lead. Craquelure is a network of tiny cracks caused by pigment shrinking due to age. When the disruption consists of perpendicular lines it is referred to as crackling.

An area of the fourth and fifth lines of text, which are written in black while the enclosed areas inside the letters are filled with blue, purple, green and yellow pigment. There are areas of brown liquid staining on both lines of text.
Bottom of folio 3r
An area of an illuminated letter at 30x magnification. The left side of the photo shows yellow pigment covered in dark cracks and decorated with red spots. A line of black ink runs vertically down the centre of the photo; the ink has a rough texture and is more thickly applied in some areas than others. To the right of the black line are three vertical rows of red spots. These are not perfectly circular but rather splodgy and uneven.
Folio 3r 30x
An area of the same letter at 100x magnification. Small pieces of yellow pigment are detaching where the cracks in it intersect with each other. The black ink sits unevenly on the parchment surface, and areas of it are shiny where they catch the light. At this level of magnification the parchment is not a uniform shade and there are dark flecks in the grey-white surface, which is very rough and uneven in texture.
Folio 3r 100x
A close-up at 20x of a letter “B” written in black ink with an outline of red spots. The surface of the black ink is very uneven, with a gritty texture. The enclosed areas of the “B” are coloured with light green pigment. A large flake of the green pigment is missing, and purple-coloured lettering from the reverse of the page shows through the parchment underneath. The parchment surrounding the letter is grey and discoloured.
Folio 3r pigment loss 20x
An area of the same letter “B” at 50x magnification. The light green pigment is mottled, and there are cracks around the area of loss. The letters showing through from the reverse of the page are clearly defined and overlaid with white cracks on the surface of the parchment. A line of black ink runs down the left side of the photo. It has an rough, uneven texture.
Folio 3r 50x

CC by Top: Lower section of folio 3r. Detail of decorated initals at 30x and 100x magnification. Bottom: evidence of loss of green pigment (verdigris or vergaut) from a decorated initial at 20x and 50x magnification. Text from the reverse (f. 3v) is shown through the parchment

For more details on the pigments used in the Lindisfarne Gospels see our previous post. The entire manuscript is digitised and available online here.

Christina Duffy (Twitter: @DuffyChristina)

06 May 2014

Recreating the Medieval Palette

In February this year the British Library hosted a course called ‘Recreating the Medieval Palette’ run by pigment expert Cheryl Porter who is also Director of the Montefiascone Project and a freelance conservator. Those of us attending were a small group of conservators and material specialists from the British Library and other institutions hoping to deepen our knowledge of the materials we work with. The course was an interesting mixture of theory and practice, with the morning lectures covering the basic colour groups and the afternoons providing a more hands-on approach giving us the opportunity to prepare and paint out the pigments and inks on a variety of papers and parchment.

Five women wearing aprons stand behind a white table. The wall behind them is grey and a lot of light is coming into the room through a large window. Two women in the middle and far right of the photo are holding paintbrushes. All are looking down at the table, on which there are small pots of green, orange and blue pigment, as well as a large beaker containing paintbrushes. Also on the table are a camera and four pieces of paper with stripes in different shades of brown, yellow, red and blue painted on them.
Recreating the Medieval Palette

CC by The group painting out some examples of earth colours made from rocks and minerals – the oldest pigments used by our ancestors

Alongside the history and manufacturing processes of the pigments we learnt about their chemical composition, visual characteristics, behaviour in response to their environment and modes of deterioration. This is essential background knowledge when undertaking a conservation treatment.

The medieval alchemists didn’t worry too much about health and safety in their search for vivid and enduring colours; hence the highly poisonous production methods for concocting pigments such as lead white, red lead, lead tin yellow, verdigris and cinnabar/vermilion. When preparing the pigments for painting, the powder has to be mixed with a binding medium to give viscosity and adhere it to the page. We experimented with different binding agents – egg white and gum arabic – which changed the working characteristics of the pigments when painted out.

A piece of paper with stripes in different shades of green, blue and grey lies on a white table top. Sitting on the piece of paper are a glass jar with a white lid and label containing a green powder, and a glass bowl containing a small amount of bright green pigment and a paintbrush. Behind the bowl and jar is a second, partially curled-up piece of paper on which two leaf motifs have been drawn in black ink.
Malachite

CC by Malachite or ‘mountain green’; a naturally mined carbonate of copper

On the left side of the photo six pots and dishes containing white, blue and yellow pigment sit on a table top covered in white paper. On the right side of the photo, on the same table top, two hands are grinding white pigment on a glass tile using a solid glass tool shaped like a doorknob.
Lead grinding

CC by Grinding lead white pigment on glass in a figure-of-eight motion

Making some of the lake colours provided an opportunity to see some real alchemy. A lake is a dyestuff made from organic matter which is precipitated onto a colourless mineral base. Plants such as buckthorn, weld and saffron were used to make a variety of colours, and insects such as kermes and cochineal produced shades of red.

A right hand mixes yellow and blue pigments on a glass tile while a left hand holds a glass jar lid above the tile. A dish of yellow pigment with a white-handled metal spoon in it sits in the bottom right corner of the photo. In the background of the photo are a jar of blue pigment and two overlapping pieces of paper, the uppermost of which has horizontal yellow stripes painted on it.
Mixing saffron

 

Two pieces of white paper lie on a grey background. Both are painted with vertical stripes in different shades of blue, which have pencil annotations above and below them.
Painted-out medieval blues


CC by Left: Experimenting with mixing saffron (yellow) with verdigris (green). Right: Painted-out medieval blues; the brighter colours are mineral-based azurite and ultramarine and the subtler shades, indigo and woad

We also had an opportunity to learn about inks used in manuscripts. This was extremely interesting from a conservator’s point of view as we discovered that inks can often be identified by the way in which they deteriorate over time. The earliest writing implements were reed pen and quill, and the group’s attempts at writing with these proved that both skill and practice were required!

 

Four people bend over a table, the surface of which is covered with cameras, notebooks, feathers and beakers of water. The two people closest to the camera are writing in black ink on pieces of white paper.
Reed pen

 

Two pieces of paper lie on a white table top, along with a quill pen, a jar of water and a block of carbon ink. The block of ink is rectangular in shape and is decorated with a white and yellow picture of a person in traditional Chinese dress. The two pieces of paper have horizonal stripes of different inks drawn on to them, and are annotated in the same inks. The annotations state what kind of ink (ivory black, lamp black, bone black) it is and what kind of pen it was applied with (quill, reed).
Quill pen

CC by Left: Practising writing with reed and quill pens. Right: A quill and block of Chinese carbon ink

Two pieces of paper on a white table top, surrounded by two jars of pigment and a beaker of water. The pieces of paper are covered in colour samples, mainly taking the form of stripes and solid blocks of colour, though there is also a pattern of interlocking circles and a picture of a bird.
Colour sample sheet

  CC by Left: One participant's colour sample sheets

 At the end of this highly informative and entertaining week we went away having learnt a lot from Cheryl’s wealth of knowledge and experience, as well as having enjoyed stories of her adventures collecting and researching pigments. Our array of sample sheets will also provide a valuable visual and chemical reference for identifying pigments in the future.

 

Vicky West

28 April 2014

As white as a...colour calibration target

The Macbeth ColorChecker(R) is often observed in digitised images adjacent to the subject being imaged. It is a colour calibration target used widely by photographers to achieve consistent colour within a studio environment. Good colour management allows the photographer to have continuity to achieve the same result with any camera. The rectangular cardboard target consists of a grid of 24 squares of colour samples, each with a measurable spectral reflectance. Reflectance refers to the fraction of incident light reflected at an interface. The spectral reflectance of these patches does not change under different lighting conditions in the visible spectrum (this is not the case in the ultra-violet and infra-red – see footnote* below), so are reliable to track colour changes in this range.

A book lies open on a black background. The left-hand page is shown and is filled with a hand-drawn picture of four medieval people in a turret with crenelated walls. Three are kneeling down, on the right side of the picture. Two of these, a man in a blue gown and a lady in a green dress and white headdress, are holding their hands together as though praying. The third kneeling figure is wearing a red tunic and blue hood. He is holding a stick and looking over his shoulder towards the left side of the page. On the left side of the picture the fourth figure, a man, is standing over the other three. He is wearing a red and green gown and a red hat or turban. Above the volume is the calibration target, which is a black piece of cardboard covered with 24 brightly-coloured squares in different colours. The squares are laid out horizontally in four rows of six. Along the bottom of the target is a measurement scale in centimetres and millimetres.

Figure 1: Calibration target shown over f.86v of Cotton Nero A.x. during imaging of Sir Gawain & the Green Knight. The target is set to be on the same focal plane as the folio. Targets are often cropped out of final processed images.

The idea of a colour chart came about in a 1976 paper in the Journal of Applied Photographic Engineering by C. S McCamy, H. Marcus and J.G. Davidson entitled A Color-Rendition Chart. The abstract states “A color chart has been developed to facilitate quantitative or visual evaluations of color reproduction processes employed in photography, television, and printing.” Their paper has been cited over 350 times to date. The original chart consisted of a 4 x 6 array of patches, each 5 cm square.

A person holds a colour chart in front of their chest. The chart fills the photo except for their hands and some surrounding areas of their black and white shirt. The chart is a black piece of card covered with 24 squares of bright colours, laid out horizontally in four rows of six. It is roughly 30cm x 20cm wide.

Figure 2: The original colour chart consisted of square patches of side 5 cm. The same size chart is still available and used today.

There are still 24 patches on modern colour calibration targets but smaller versions are now available with patches measuring 1 cm wide. The X-Rite ColorChecker(R) Classic target used in our lab is shown below with a scale, focusing target, and reference number that we attached.

A rectangular piece of black card with 24 squares cut out of it is laid over 24 squares of bright colour. The squares are laid out horizontally in four rows of six. A measurement scale in centimetres and millimetres runs along the bottom edge of the black card, to the right of the word “MegaVision” printed in white, and a small white rectangle filled with a combination of lines and numbers. The serial number 130901 runs vertically up the left edge of the card.

Figure 3: The ColorChecker(R) Classic target has 24 colours in a 6 x 4 grid. The colours are painted in matte on smooth paper and surrounded by a black cardboard border. 

The colours are roughly divided into four kinds. The top row is composed of colours which approximate natural objects such as human skin (dark and light), blue sky, the green colour of a leaf, and a blue chicory flower. The second row is made of miscellaneous colours encompassing a good range of test colours. The third row is comprised of the primary (blue, green, red) and secondary (yellow, magenta, cyan) colours, and the fourth row represents a uniform gray lightness scale ranging from brilliant white to black.

A chart with four columns. In each column are six coloured squares, with the name of the colour written to the right of the square. The text is in black on a white background.

Figure 4: Colours in the calibration target. These colours are precisely measured and can be described in terms of the Munsell color system (a colour space describing colours in terms of their hue, lightness and chroma).

Larger colour calibration targets do exist such as the ColorChecker(R) Digital SG which boasts a gamut of 140 colours.

A dark grey rectangle with rounded corners, covered with 140 brightly-coloured squares laid out horizontally in ten rows of fourteen. A 6cm measurement scale is in the bottom right corner of the rectangle. In the bottom left corner of the rectangle the word “gretagmacbeth” is printed in light grey. Along the top of the rectangle the words “Digital ColorChecker SG” are printed in light grey.

Figure 5: ColourChecker(R) Digital SG boasts the widest colour gamut available. Its design is based on the original ColorChecker(R) target but is enhanced for digital photography. Image copyright X-Rite, from X-Rite website.

For consistent colour, photographers can take a shot of the calibration target with the camera set to capture raw files. Shooting raw is the only way the camera chip can capture all of the information available in the scene. The image is opened in image processing software such as Photoshop, and a script is run on the image which opens it multiple times with different settings. Results are measured and a status is generated with values which can be used to fine-tune the camera’s colour calibration and get processed colour to match the original scene (or alternatively to distort the colour for special effects!).

While colour calibration targets are on the whole produced in the same way using the same materials, on average, every colour target is ever-so-slightly different. The colour difference may be very small and only measureable using other scientific methods. Colour difference is a metric of interest in colour science - the standard metric being Delta E (ΔE). This definition allows colour difference to be quantified in a way which is more reliable than just using adjectives, a practise which is detrimental to anyone whose work is colour critical!

Our multispectral imaging system captures images in Lab colour space, where L is lightness and a and b are colour-opponent dimensions. Lab colour space approximates human vision and is device independent. It includes all perceivable colours with RGB and CMYK spaces (see our previous post What the CMYK? Colour spaces and printing) sitting within its larger gamut, so file sizes are generally much larger. Values for L, a, and b can be tracked once the image has been white balanced using the white colour patch on our calibration target as a reference. However, Lab files don’t open in all software packages so quite often it is necessary to transform images into other spaces such as RGB, but the original Lab file is always stored.

Colour Science is a fascinating and growing area of research. For fun you can try out this Color IQ test from the X-Rite website to learn more about how you see colour, and to find out where you can get your own targets.

 

Christina Duffy (@DuffyChristina)

Footnote:

*While the Macbeth ColorChecker(R) provides 24 colours with consistent spectral reflectance under typical lighting conditions in the visible spectrum, it does not behave similarly in the ultra violet or infrared parts of the Electromagnetic Spectrum. Another material such as Spectralon is required for imaging outside of the visible range. The property which defines a diffusely reflecting surface (i.e. an ideal “matte”) is called Lambertian reflectance and Spectralon exhibits highly Lambertian behaviour with a spectral reflectance of >99% from 400-1500nm and >95% from 250-2500 nm. Spectralon is a fluoropolymer - others include PVF, PVDF and PTFE (Teflon). Spectralon has the highest diffuse reflectance of any known material over IR (infra-red), VIS (visible) and NIR (near-infrared) regions of the spectrum, and is therefore very expensive, but necessary to track colour difference during multispectral imaging.

Reference

McCamy, C.S.; Marcus, H.; Davidson, J.G A, 1976, A Color-Rendition Chart, Journal of Applied Photographic Engineering Volume 2, Number 3, pp 95-99

X-Rite website, or follow X-Rite on Twittter

26 March 2014

Cleaning and rehanging the Kitaj tapestry

The R. B. Kitaj Tapestry If not, not was rehung in the St Pancras Entrance Hall last Monday night after being removed for intense conservation cleaning. The tapestry is based on the painting of the same name by R.B. Kitaj, and measures 6.75 metres high and 6.75 metres long; it was the largest in the world when created by the Master Weavers of the Edinburgh Tapestry Company for the British Library. The tapestry had not been cleaned since its installation at St Pancras in 1997 and was displaying visible surface dust which had to be removed.

A wide birds eye view of the British Library’s large and open foyer with the Kitaj tapestry hanging on the brick wall straight ahead. The tapestry is flanked on either side white architectural features, to the left are open plan levels and winding staircase, to the right are two tall white pillars which merge into the upper mezzanine.
View of the British Library foyer with the Kitaj Tapestry hanging on the wall

CC by The Kitaj tapestry

The tapestry was taken down on 28 September 2012 by Collection Care staff guided by experts from Textile Conservation Ltd. who would undertake the mammoth task of cleaning at their studio in Bristol. 

This image shows a long tube covered in a white material called Tyvek, lying on a brick and white tile floor. This is the inner role used to support the tapestry once taken down off the wall. The floor has sheets of white protective material laid out in rows parallel to the tube, which will be wrapped around the tapestry once on the tube for safe transport and handling.
The tapestry was taken down and rolled before being taken away for intense conservation cleaning

CC by 

Samples of thread of various colour and locations were removed to monitor fading and colour change in the tapestry. A remarkable eight miles of  warp was threaded vertically between steel rollers during its production.

The tapestry is on protective material on the ground and piled on top of itself, showing off the vibrant colours and needle work of the back of the tapestry.
View of the vibrant threads on the back of the tapestry after being removed from the wall.

CC by 

The tapestry was originally hung using lengths of beige hook and loop fastener. Six lengths divided into three pairs (10 cm apart) were stitched along the top edge. Along the sides were lengths measuring about 55 cm with gaps. These lengths were removed and the turned in sides were released by cutting and removing the stitching. It was here where casings from carpet beetle larvae and degraded moth cases were found. Luckily these were desiccated and no signs of damage were apparent. (Read more about how we deal with pests in a previous post: The Bookie Monster: attack of the creepy crawlies!).

Where to start with cleaning such a huge tapestry? With a hoover of course! The optimum level of suction was determined and the entire front and back surfaces were cleaned using a low powered vacuum suction. The hoover dust consisted of fine dust, brick dust and larger fibrous dirt found mainly on the front. This bag of dust has been retained by Collection Care staff for further scientific analysis. We are very serious when it comes to dust as you may have read in A-a-a-chooo! Collection Care’s Dust Busters.

Once clean it was important to ensure that no insects or eggs remained in the weave. The tapestry was rolled and taken to Harwell Document Restoration Services where it was placed in a freezer unit at -18°C for two weeks. It was fully defrosted over four days and taken back to Textile Conservation Ltd. where a new lining and Velcro hanging system were attached, as well as reinforcement work on any loose stitching. It was then rolled with interleaving layers of tissue and wadding and wrapped in Tyvek and bubble wrap before making its way back home to the British Library.

The tapestry was scheduled to be rehung on the opposite wall to where it was originally placed providing a wider range of viewing angles, and allowing visitors to get up-close to the tapestry on the stair levels. An impressive scaffolding system was erected and new battens were attached to the wall. The tapestry was hoisted up to the top platform after a thorough treble check that it was facing the correct way around!

A view of a five-level scaffolding installed in front of a red brick wall where the tapestry once was.
Scaffolding assembled.

CC by The tapestry was placed on the upper platform when the scaffolding was fully installed

The Textile Conservation Ltd team took the top platform and began by attaching the top Velcro strips to the horizontal battens.

Close up of two conservators in yellow high vis. vests standing on scaffolding by the red brick wall, one conservator is standing on a level of scaffolding above the other. They both have their hands extending outwards towards the wall, where they work together to apply a protective material on top of the Velcro battens before the tapestry is lowered. This will allow a safe and controlled lowering and attachment of the tapestry.
Conservators preparing for the reinstallation of the tapestry

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The tapestry was then carefully lowered down in stages by scaffolders. 

A side angle of the reinstallation and lowering of the tapestry, with two staff standing together on a level of the scaffolding. The protective material has. Been removed slightly to allow connection between the verso of the recently conserved tapestry and the Velcro battens.
Lowering the tapestry

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This provided a controlled unrolling allowing Collection Care staff to hook the sides onto the battens without any air gaps.

Three conservators standing on scaffolding hands extending out and supporting the tapestry together, as they slowly lower it and attach it to the Velcro batons.
Protective tissue paper was removed as the tapestry was unrolled.

CC by Protective tissue paper was removed as the tapestry was unrolled

When the scaffolding was removed a few days later the final result was terrific!

Close up of the tapestry after conservation back on the wall.
The R.B. Kitaj tapestry

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The tapestry has regained its vibrancy of colour and is a magnificent feature in the British Library Entrance Hall. You can read more about the construction of the tapestry in this Telegraph article from 1997, and more about the artist in the National Galleries of Scotland website.

Christina Duffy

24 March 2014

Father Kögel and the ultra-violet examination of manuscripts

2014 marks the hundredth anniversary of another important event: the first use of ultra-violet radiation for the examination of manuscripts, and particularly the deciphering of palimpsests. Scholars are frequently challenged by manuscripts which have faded to the point of illegibility, or which have been deliberately erased, or, most challenging of all, which have been erased and then written over. The Archimedes Palimpsest is one of the most famous recent examples, but palimpsests have long been exercising the minds and eyes of scholars, certainly since the middle of the 19th century.

The Manuscript is opened up about half way through the text block, with grey cuboid foam supports under the front and back covers.  The book is a medium size, able to handle in both hands, but is very thick. The opening looks quite dirty and worn, with. purple, orange, and brown patches of discolouration. The written text is very small, neat and organised. The left page looks as though there has been previous repair, with an extension or boarder added to the fore edge and bottom edge so that it is uniform size with the rest of the text block.
The Archimedes Palimpsest is a medieval parchment manuscript, now consisting of 174 parchment folios

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Early attempts to make unreadable manuscripts readable, dating from the 18th century, used chemicals that would react with traces of iron in the fibres of the parchment which remained after the iron gall ink used to write the text had faded or had been removed. The trouble with these techniques was that, while they might initially be successful, they ended up staining the parchment blue or brown, leaving it even less legible than it was to begin with.

Photographic techniques had also been used to enhance faded writing almost since the invention of photography in 1839. In 1894 a process was developed for revealing palimpsests which used two plates: an over-exposed plate which would show both the upper and the lower writing, and an under-exposed plate that would show only the upper writing. A positive made from the under-exposed plate could then be used as a mask to permit an image of the lower writing only to be made. While this process was successful, it was time consuming because two plates had to be made, and their registration had to be very accurate in order for the upper writing to be cancelled out as nearly as possible.

In 1914, Father Raphael Kögel OSB published a paper in the Reports of the Royal Prussian Academy of Sciences in which he explained how ultra-violet radiation from an electric arc or a mercury vapour lamp could be used to excite fluorescence in parchment, but the fluorescence would be blocked (quenched) where the ink had originally been. A photograph of the visible fluorescence could then be taken, using filters to exclude the invisible ultra-violet which would obscure the image. This paper was in distinguished company: other authors in the same volume included Einstein and Planck. UV fluorescence photography should be distinguished from UV photography: in UV photography an image is made of the invisible ultra-violet radiation reflected from the manuscript; in UV fluorescence photography an image is made of the visible light emitted by the manuscript where it has been excited by ultra-violet radiation.

Father Kögel was born Gustav Alfred Kögel in Munich in 1882; he took the religious name of Brother Raphael when he joined the Benedictine abbey at Beuron, in the south of Baden-Württemburg, in 1898. He was sent to Brazil as a missionary, but fell ill and had to return to Germany. He then entered Wessobrunn Abbey, south-west of Munich, and was ordained priest in 1906. He later studied chemistry in Vienna, and in 1912 began working with the Palimpsest Institute at Beuron, which had been set up by Father Alban Dold specifically to study the Abbey’s rich collection of Carolingian and other medieval manuscripts. Here he developed his ultra-violet imaging techniques. He had previously experimented with coloured filters and photographic plates with different spectral sensitivities to improve the visibility of the under-writing, and also with chemical methods for enhancing faded writing, even though these had been condemned at the St Gallen conference on the conservation of manuscripts more than ten years before (“… this barbaric method …”).

Kögel became a professor at the University of Karlsruhe in 1921, and set up an Institute for Technical Photochemistry and Scientific Photography. Whether because of a crisis of faith, perhaps caused by the war, or simply because he found the academic life more congenial, Kögel left the church in 1922 and married in 1924. Kögel made important advances in using UV examination in forensics, and was also a pioneer in X-ray fluorescence analysis. His greatest commercial success was the development of the Ozalid diazo photocopying process, which was widely used until the 1970s. He died in 1945.

Because of the outbreak of war, Kögel’s publication does not seem to have been noticed in English-speaking countries until the early 1920s. For example, the first edition of C. A. Mitchell’s Documents and their scientific examination (1922) does not mention the use of UV, while the second edition (1935) does. Awareness of the technique grew in the 1920s and its use was well established by the 1930s. R.B. Haselden’s Scientific aids to the study of manuscripts, published by the Bibliographical Society in 1935, gives several examples of palimpsests that had been revealed by UV photography. He warns that users should wear protective goggles and protect their skin against excessive exposure to UV, and also that “prolonged exposure to UV light is injurious to a manuscript”. Unfortunately this message was not taken on board by everybody, and I have seen manuscripts where features that were seen and photographed under UV in the 1930s are no longer visible today. Haselden advises against the use of chemical reagents to restore faded ink, but goes on to recommend the use of a solution of anthracene in alcohol (“perfectly harmless”) to enhance faded writing – the solution penetrates the paper or parchment more rapidly where there is no ink, so the writing stands out against the vivid fluorescence of the anthracene under UV. Other writers recommend the use of a mixture of Vaseline and mineral oil for the same purpose, but it hardly need be said that these techniques are not recommended.

For best results, UV examination needs to be carried out in a darkened room, using a good-quality UV lamp and while wearing UV protection glasses. It has not always been thus. My wife remembers that when she was researching in a very well-known library in the 1970s, there was only one electric socket into which a UV lamp could be plugged, and this was underneath a table. She was therefore obliged to lie underneath the table with her manuscript and the UV lamp, sometimes with a member of the library staff to invigilate.

A close up of the left side page of an open book, showing the verso of the page. An off-white paper boarder surrounds a white sheet, which appears to be a support for a fragment that would be fully visible from the recto. The centre of the white sheet has been cut-out to match the shape of the fragment. The black verso of the fragment is visible, and is being held in place with an off-white tape or Japanese tissue. Surrounding the black shape of the fragment, on the paper support are patches of discolouration in a distinct shape, possibly staining from a fragment in contact with the paper on the facing page.
Folio 54 verso without UV illumination
A close-up image of the verso of the fragment illuminated with a UV light. This. The paper, fragment, and repair tissue have all gone different shades of bright and vibrant blues. The UV light has been able to illuminate text as the ink is invisible to the naked eye.
Folio 54 verso with UV illumination

CC by The Electronic Beowulf project experimented with ultraviolet, first scanning fol. 54 verso under an ultraviolet lamp with a Kontron digital camera

UV examination is now being superseded in libraries such as the British Library which own multi-spectral imaging equipment. This gives better results as it can be much more selective than any process using filters to choose the wavelengths of fluorescence that are photographed. It uses much shorter exposures and therefore minimises the risks of exposing manuscripts to intense ultra-violet radiation. (See Christina Duffy’s blog post ‘Revealing hidden information using multispectral imaging’)

Dr Barry Knight, Head of Conservation Science & Research

 

References

Haselden, R.B., Scientific aids to the study of manuscripts, Supplement X to Transactions of the Bibliographical Society, 1935.

“Kögel, Gustav”, in Neue Deutsche Biographie 12 (1980) 295-6. www.deutsche-biographie.de/sfz43637.html

Kögel, P.R., Die Palimpsestphotographie, Sitzungsberichte der königlich Preussischen Akademie der Wissenschaften, 1914, 974-978

Mitchell, C.A., Documents and their scientific examination. London: C. Griffin & Co. (1922).

16 March 2014

The Colour Green

With St Patrick’s Day upon us it seemed fitting to take a closer look at some green pigments used throughout art and history.

Green earth pigment

Green earth pigment (or Terre Verte, Stone Green, Verdetta, Celadonite) is composed of clay coloured by iron oxide, magnesium, aluminium silicate, or potassium. The clay was crushed, washed and powdered. It was used since the time of the Roman Empire until the end of the Renaissance and was highly popular in medieval painting, especially for underpainting of fleshtones. An example is shown below in The Annunciation (1398-1311) by Duccio di Buoninsegna. Here faces were first painted with the green pigment and then overlaid with pink to give a realistic hue. In this case the pink has faded giving the impression of green skin. Green earth pigment was sourced from regions in the south of France and in Italy around Verona.

 

 Gabriel dawned on light purple and light blue garments standing to the left of Mary facing her straight on. Mary dressed in a luscious and rich ultramarine robe and vermilion dress stands on the right with her body facing the viewer with her face looking toward Gabrial. They are set in simple and articulated architectural surroundings. The architectural setting is made to mimic three dimensionality with crude perspective and bold shadows and highlights. Gabriel is depicted motion, his right leg extended back with his foot just about to lift from the  ground, and his right hand extended out towards Mary, his hand  gesturing the peace sign. Mary appears to pull back, with her left arm covering her chest reaching over her shoulder to gripon to her robe. Her left arm hangs down beside her body holding the bible open with text. Above and in between Gabriel and Mary is a  white  dive with rays of light  representing the Holy Spirit shining towards her.
The Annunciation by Duccio di Buoninsegna: The Archangel Gabriel announces to the Virgin that she will be visited by the Holy Spirit and bear the son of God. Held at the National Gallery

 

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Malachite

Malachite is a copper carbonate hydroxide mineral (copper(II) carbonate), and is green due to the presence of copper. It was used as a mineral pigment in green paints from antiquity until about 1800. It is fairly lightfast and very sensitive to acids meaning its colour can vary.

 

An extreme close  up and zoom of green malachite. It has two vivid textures, one has the appearance of moss which is a dark green, and makes up the majority of the malachite sample.  The  second texture is smooth and  round lighter green bundles, which look like the heads of baby mushrooms. The sample has the appearance of fistfulls of the moss texture being piled ontop and beside of each other, with the small round and smooth bundles placed in between the rough topography of the sample.
Brazilian malachite specimen highlighted by spheroidal rosettes of azurite (source) 


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Artist Pietro Perugino used finely ground malachite in his 1503 painting Nativity to colour the bright green garments of the worshippers. 

 

Four wise men kneel to the left of and behind the baby Jesus who is lying on a purple cloth facing the viewer while Mary kneels to the right of him. Their hands are raised  to their chest in prayer, except for one wiseman farthest to the right who has his hands raised to his chest in motion, as if exclaiming with stunned joy. Directly behind them is an ornate four post gazebo, with a cow lying down and a donkey  standing on the far left side of the painting. The backdrop to the scene is a wide and open pastoral view, with green fields and few trees in the far distance. Rolling hills flank the sides of the background fading out to a light blue illusting great depth and space.
Green pigment malachite is found in Nativity by Pietro Perugino (1448-1523)

 

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Malachite has also been found in the King George III copy of the Gutenberg Bible, held at the British Library using Raman Analysis.

 

Close up of a single sheet with two columns of neat bold text inblack  ink with red ink headings. Ornate embellishments are painted between the columns of  text and surrounding the, like a sideways 8 looping around everything. The embellishment is a floral theme with vines swirling around and flowers stemming off, with colourful birds and a monkey perched throughout the vines. The substrate is a pale beige colour and is in very good condition, with just some engrained dirts visible around the edges.
Gutenberg's (42-line) Bible: Opening of Proverbs. Johann Gutenberg, Johann Fust and Peter Schoeffer. Mainz, 1455 British Library C.9.d.4, f.1. Copyright the British Library Board

 

 

Cobalt green

Cobalt green is a moderately bright and translucent, but highly permanent, green pigment. The compound is formed by heating a mixture of cobalt (II) oxide and zinc oxide and was discovered in 1780 by Swedish chemist Sven Rinman. It can be mixed with other pigments and is also known as Rinman’s Green or Zinc Green.

 

Close up of ground cobalt green pigment, in a loose powder.
Cobalt green (source)

 

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Cobalt green was never very popular due to its high cost and weak tinting power. Researchers at the University of Washington have discovered that cobalt green possesses special magnetic properties and is now being used in the field of spintronics. Spintronic devices are used for computer storage and memory. Cobalt green has found success with spintronic devices as it can be used at room temperature while other materials must be super cooled.

Verdigris

This is a basic copper acetate and is formed when copper is exposed to acetic acid vapours.  The natural patina that forms on copper roofs is often called verdigris, but in non-polluted areas it is in fact malachite (basic copper carbonate).  In polluted areas, though, it is antlerite, a basic copper sulphate.  They are all similar colours so are easily confused, but verdigris in particular causes problems in manuscripts – it goes brown and can burn through the parchment and cause staining on adjacent folios. Verdigris has been used on murals in Pompeii, throughout the Renaissance and on medieval manuscripts including the Lindisfarne Gospels and Book of Kells.

A light aquamarine colour, in powder form, is in a clear glass jar with a black lid, sitting on a black table with white background.
Verdigris (source) 

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Verdigris was found to be unstable and unwilling to mix easily with other pigments. In fact the great Leonardo da Vinci warned against its use in his treatise on painting and was leter replaced by the more stable Chrome Green.

Close-up detail of paint layer. Three spots of an opaque mustard colour paint sit on top of large areas of  a transparent glass-like turquoise colour, which has many small cracks. Many of the cracks look like misshapen rectangles and triangles. Surrounding the turquoise is a line of black, with some areas having a higher sheen, and some areas looking mat, with small areas left abraded, now missing pigment. Above this is an area painted with a chartreuse yellow, also with many small cracks.
Verdigris has been used to decorate the initials on f44v of the Lindisfarne Gospels shown here at 50x magnification (see here for more microscopy images of the Lindisfarne Gospels)

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Viridian

Viridian was patented in 1859 and is a hydrated chromium(III) oxide Cr2O3 pigment described as a dark shade of spring green.

Close up of powdered veridian, apple green in colour. The head of a silver spoon is holding a spoonful of the powder above the pile of veridian.
Viridian (source)

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Viridian was used by Vincent van Gogh in many of his works including Café Terrace at Night, 1888 (Kröller-Müller Museum, Otterlo) and the Night Café (Yale University Art Gallery). Van Gogh to his brother Theo in 1888: "I sought to express with red and green the terrible human passions. The hall is blood red and pale yellow, with a green billiard table in the center, and four lamps of lemon yellow, with rays of orange and green. Everywhere it is a battle and antithesis of the most different reds and greens.” [1]

The Night Café

CC zero Artist Vincent van Gogh (1853-1890) The Night Café, 1888. Oil on canvas currently at Yale University Art Gallery

In many cases a combination of pigments was used to create green colour. Recent analysis of the Sir Gawain and the Green Knight manuscript have shown that indigo (blue) over orpiment (yellow) was used in some areas, while a single mineral green was used in others.

Painting of a man with scruffy blond hair on loose black garb. Both his hands are extending to the left holding a battle axe. The background seems to have quite a bit of pigment loss, showing a yellowish ground coming through where loss of the dark green paint has been abraded or scraped away. There are two large dark green vases on either side of the man, with crude red and white flowers sticking out.
 Sir Gawain and the Green Knight, Cotton Nero Ax folio 129v

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Christina Duffy

Reference: [1] Vincent van Gogh, Corréspondénce general, number 533, cited by John Gage, Practice and Meaning from Antiquity to Abstraction

13 March 2014

CSI at Festival of the Spoken Nerd: I Chart the BL

The British Library Science Team in collaboration with Festival of the Spoken Nerd put on a highly entertaining event last Monday night entitled I Chart the British Library. The event explored the highs and lows of data visualistion and was sold out attracting over 250 people to the British Library Conference Centre.

The show is part of a season of events at the British Library supporting the stunning exhibition Beautiful Science: Picturing Data, Inspiring Insight.

A large group of people in a conference room, most are standing but some are sitting around two round tables at the front of the photograph. Many people in the group have both hands raised upwards.
Hands up if you think science is cool!



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The show was hosted by stand-up mathematician Matt Parker, geeky songstress Helen Arney and science experimentalist Steve Mould. The hosts were joined onstage by the British Library’s Head of Sound & Vision Richard Ranft who showed the audience some wonderful examples of how animal and bird sounds were historically recorded using musical notation – a lot different to how sounds are recorded today!

Collection Care was represented during the interval by a demonstration of the Library’s very own CSI team – Conservation Science Imaging of course! Audience members tested the contents of their wallets both under the microscope and under a multispectral camera to delve into anti-fraud techniques. The first thing we noticed was that some pound coins had the initials IRB under the Queen effigy, while others didn’t.

A group of people stood around a woman seated by a desk with a laptop and photographic stand equipment set up. The camera is acting as a microscope, visible on the laptop, to better visualise banknotes and coins.
Analysing notes and coins during the interval

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The £1 coin below on the left shows a portrait by Raphael Maklouf in which the Queen wears the George IV State Diadem. This design was in use between 1985 and 1997 after which a competition was held by the Royal Mint to design a new effigy. The winner was Ian Rank-Broadly and his design (right) shows the Queen wearing the ‘Girls of Great Britain and Ireland’ Tiara, with a signature-mark IRB below the portrait. To date three different obverses have been used.

Two british pound coins heads-up side by side on a  grey background. The coin on the left dating to 1990 with a portrait by Raphael Maklouf in which the Queen wears the George IV State Diadem. The coin on the right dating to 2001 with a portrait by Ian Rank-Broadly showing the Queen wearing the ‘Girls of Great Britain and Ireland’ Tiara. The IRB signature mark is found on this coin
Two one pound coins



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IRB are the initials of the British sculptor Ian Rank-Broadly who has produced many designs for British coinage. The initials are difficult to make out with the naked eye but under the microscope they are clearly observable. Things to look out for in the case of counterfeit coins include date compared to design, edge lettering, quality, and orientation (the designs on both sides of the coin should be aligned when swivelled).

Extreme zoom at 200x magnification of a section of a coin, dark silver in colour, showing the relief of the initials I R B. The initials IRB stand for Ian Rank-Broadly and sit under the effigy of Elizabeth II on coins from 1998 onwards.
Close up of letters on a coin



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“But what about hard cash?” asked one audience member producing a twenty euro note. "To the multispectral camera – poste-haste!" The design on the bank note is created using a variety of inks. Each ink has a unique spectral reflectance and so different parts of the design appear and disappear at different wavelengths as we move from ultraviolet (UV), through the visible (VIS) region and into the infrared (IR) part of the electromagnetic spectrum. Notes which don’t behave in this way are most likely counterfeit. Luckily no fakes were found!

A 20 euro banknote shown four times with different lighting. The top left is a twenty euro note in normalighting, showing a note with various  shades and hues of purple, the imagery of elaborate stained glass windows as the banknote image. The top right shows the 20 euro note at 420 nm (UV, this results onan image of the bank note in black and white with strong contrast. The bottom left shows the bank note in 700 nm (VIS) lighting. This results again in black and white, with a softer contrast. The bottom right shows the note in 1000 nm (IR) lighting, again resulting in a black and white image, however it has the appearance of being over exposed, very pale with almost no contrast.
A 20 euro bank note in different lighting wavelengths



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Audience members were also invited to visualise sounds using spectrographs and to participate in a live analogue data collection and visualisation experiment conducted by Matt Parker.

A man in blue trousers and a black leather jacket stands with his back to the viewer in front of a whiteboard, with his arms outstretched. A man also with his back facing us, but appears closer to the viewer seen only from the waist up in a blue jumper. The whiteboard in the background has a list or vertical timeline on the left safe barely visible in red and green marker, and on the right hand side has large half circles drawn in red and green marker.
Matt puts his volunteers through their paces in this live experiment



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The goal was mapping back-to-back distributions of female vs male arm spans and a fantastic 137 people took part. The Libation Lab (or bar…) was also a huge hit and really made everyone appreciate all those sciency puns.

The night was a huge success and I think we all learned something new - well done to the BL Science Team! You can read more about their experience on the science blog.

Visit the Beautiful Science: Picturing Data, Inspiring Insight exhibition until 26 May 2014 in the Folio Society Gallery for free.

Christina Duffy

16 February 2014

Sea Snails and Purple Parchment

Purple coloured pages of vellum are sometimes found in sacred texts adorned in gold or silver lettering. They can be seen in folios 2-5 of the recently digitised Cotton Titus C XV on the British Library's Digitised Manuscripts website. Fragments of the Codex Purpureus Petrolpolitanus (a 6th century copy of the Four Gospels in Greek) demonstrate the use of purple as an indicator of wealth, power and kingship. Purple parchment was once only used for Roman or Byzantine Emperors, but later found use in Anglo-Saxon illuminated manuscripts for the Emperors in Carolingian art and Ottonian art. The discovery of shell fragments in archaeological sites in Scotland and Ireland has pointed to the harvesting of sea snails for a gland which produces the purple colour. 

A close-up of single folio lays on a dark grey surface. The parchment folio is a warm caramel colour, mottled with darker and lighter areas. There are some subtle patches of purple colour, leaving evidence of its original colour. There are two columns of very organised, neat silver-grey text, with very bold and graphic letters. In some areas, letters are visible between the lines of text, showing through from the other side. The texture of the parchment shows itself through small wrinkles and a grain pattern. The right edge shows evidence of previous sewing holes with semi-circular losses. The left edge shows small losses and wrinkles along the edge, and a small loss no the bottom corner.

Figure 1: Fragment of the Codex Purpureus Petropolitanus, 6th century, Cotton MS Titus C XV, f. 4v. Read more about this codex on the BL Medieval blog: A Papyrus Puzzle and Some Purple Parchment. 

In 1992 marine shell remains were recovered from caves in Sutherland County in Scotland. Archaeologists used sieves to isolate shells of the whelk known scientifically as Buccinum undatum. These whelks survive in shallow water (down to about 100m) and are found in sand and mud. Their usual capture occurs using baskets or baited pots. The fragmented state of the shells dispersed around the site suggested that they had been purposely collected and broken.

A close up of two sea snail shells on a black background, which share a similar shape to an ice cream cone, if the ice-cream scoops got smaller and smaller. One sea shell faces down, while the other is faced up, showing the cavity for which I sea snail would inhabit. They are both varied colours of sand and warm caramel and pinkie colours. There are small horizontal lines cutting through the shells like a shallow engraving, with larger smooth vertical waves flowing length wise down the shell.

Figure 2:  The sea snail Buccinum undatum.

Another type of whelk mollusc, known as Nucella lapillus (dogwhelk or Purpura lapillus) was found at the Scottish site in Wetweather Cave. Nucella lapillus are found in crevices around rocky shores and estuarine conditions. They are a species of predatory sea snail found around the coasts of Europe and in the north west Atlantic coast of North America where they feed on barnacles and mussels. The deliberately broken shells indicated to researchers that the whelks, which are not edible and were not being used as fishing bait, were being gathered for the production of purple dye.

 About 18 white, grey, black, brown and yellow coloured sea shells, same shape as described above.  They lie on top of a rough grey stone background with evidence of barnacles from their honeycomb like structures attached to the rocks in a single layer sporadically laid out. These seashells are alive with sea snails inside – not visible in this image – and they are feasting on the barnacles.

Figure 3: Nucella lapillus feeding on barnacles. 

Nucella lapillus was also found in Connemara in the West of Ireland in 1919 by J. Wilfred Jackson. Heaps of shells (referred to as Purpura-mounds) had previously been found in 1895, but Jackson noted that the shells had deliberately broken apical whorls (a whorl being a turn of the whelk's spiral shell), but the lower whorl with the mouth had been left intact. The shells were smashed in such a way as to retain the cumella allowing the beast to be removed easily. It was clearly a serious business with one of the Irish Purpura-mounds measuring about 50 by 14 m  - over 200 whelks were found in a single square foot!

The dye is comprised of a mucous secretion from the sea snail's hypobranchial gland and is an organic compound of bromine. The secreted fluid is released by the sea snail as a defence mechanism when agitated. The secretion can be collected by "milking" the sea snails, however this is a very labour intensive process and more often than not the snails are crushed instead. It can take thousands of snails to produce a single gram of pure dye. After salting, boiling and sitting for a few days the gland fluid begins to turn from a pale cream to a purple colour. This process is accelerated by sun exposure. After about 10 days the dye is ready for use.

A single page from a manuscript, with a dark purple background and white and yellow writing. The writing is very nest and organised and quite square and graphic in appearance.  There are two white graphic elaborations on the left-hand side one above the other with some space in between. On the bottom of the page are four arches painted in white with yellow and white initials placed inside of each arch. The condition of the folio is in very good condition, with a small loss in the bottom right corner, and a larger but still minor loss on the top left corner.

Figure 4: A purple parchment page of the 6th century Codex Argenteus with gold and silver lettering. 

Christina Duffy  (@DuffyChristina)

 

Further reading

Pollard, Tony (2005) 'The excavation of four caves in the Geodha Smoo near Durness, Sutherland'. Scottish Archaeology Internet Report 18

Jackson, J.W. (1917) 'Shells as Evidence of the Migrations of Early Culture'

Henderson, George, Vision and Image in Early Christian England, Cambridge University Press, 1999, paperback edition 2010, Chapter 3, pp.122-135, 'The Colour Purple: A Late Antique Phenomenon and its Anglo-Saxon Reflexes'.

03 February 2014

I’ve got tone, halftone: under the microscope with a printing block

As an Imaging Scientist it is very difficult to look at ordinary objects without wondering what they would look like under a microscope. This was just the case when shown a beautiful printing block with a portrait of Steve Fairbairn, founder of the Head of the River Race, etched on the front. Printing blocks like these were used alongside similar-sized blocks containing type in a printing press to commercially produce images and text for publications. But how does it work?

Image shows printing block of Steve Fairbairn, it is a reddish metal plate (consisting of lead tin and some antimony) with a copper electrolytic layer). It is attached with steel screws to a 21mm thick light colour wooden block.
The Fairbairn printing block, belonging to Pauline Churcher of Thames Rowing Club, consists of type metal (lead, tin and some antimony) with a copper electrolytic layer attached with steel screws to a 21 mm thick wooden block

 

The left of the Image depicts cream envelope used to store printing block with graphite inscription. To the right of the image is the printing block of Steve Fairbairn
The Fairbairn printing block, belonging to Pauline Churcher of Thames Rowing Club, consists of type metal (lead, tin and some antimony) with a copper electrolytic layer attached with steel screws to a 21 mm thick wooden block


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The traditional printing method of letterpress is capable of printing solid colour from printing plates. In order to convey an image with varying shades and tones using a single colour, a reprographic technique called halftone is used. Halftone simulates continuous tone through the use of dots of various sizes, shape and spacing. The image is broken up into many small solid areas for printing. This gives the illusion of a continuous tone – but if we look up-close, we can see that the image is just an intricate pattern of dots.

Halftoning is a term used in the print industry to describe how to reproduce varying tones with significantly fewer inks. Image at the top shows the gradient and the image at the bottom shows a close up of the dots that make up the gradient
Halftoning and halftoning close up: A series of dots of various sizes creates an optical illusion of continuous tone when viewed from a distance


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This pattern is created using a printing block with tiny holes etched into a metal plate where ink can sit and be transferred onto paper. Below we see what the Fairbairn printing block looks like at 20x, 50x and 200x magnification.

Image shows the printing block at x20 magnification. Depicting the portrait of Steve Fairbairn, at 20x magnification you can see Fairbairn's eyes and nose and the dots that make up the image are starting to appear
The Fairbairn printing block at 20x magnification. These three images show the increasing magnification of halftone detail on the printing block (top 20x, centre 50x, bottom 200x). Ink is brushed over the plate and fills the hollows.
Image of the printing block at 50x magnification, the dots are now very clear. The dots are a bluish hue and the background the reddish metal
The Fairbairn printing block at 50x magnification. These three images show the increasing magnification of halftone detail on the printing block (top 20x, centre 50x, bottom 200x). Ink is brushed over the plate and fills the hollows.
Image shows the printing block at 200x magnification. The holes are very clear now with a bluish appearance surrounded by the reddish metal. These holes would be flooded with ink when it was brushed over the plate.
The Fairbairn printing block at 200x magnification. These three images show the increasing magnification of halftone detail on the printing block (top 20x, centre 50x, bottom 200x). Ink is brushed over the plate and fills the hollows.

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Before the inception of halftone printing, images were printed in books and periodicals using hand engraved metal plates or wood blocks. Wood engraving involves working an image or group of images into a block of wood for use as a printmaking and letterpress technique. Ink is applied to the face of the block and paper is pressed against it.

In ordinary engraving such as etching, a metal plate is used and is printed by the intaglio method where the ink fills the removed areas. When the excess ink is wiped away a sheet of paper is placed on top of the plate, and a blanket covers both to ensure even pressure when pressing. The paper is pushed onto the ink creating an image.

The idea of halftone printing is attributed to William Fox Talbot in the late 1850’s. There were many different methods to produce the halftoning effect, and the earliest trials involved directly etching the images formed on Daguerreotype metal plates. However, the time and skill required to perform such an etching, the inability to print images next to type, and the quick to wear out fragile plates, meant that the process was impractical for commercial publishing. The turning point came in 1881 when Frederic Ives patented a commercial halftone method in the United States.

Black and White Image of Frederic Ives, circa 1899. The image shows Eugene inserting Kromogram into his Kromskop which is resting on a table in front of him.
Frederic Eugene Ives inserting a Kromogram into his Kromskop, circa 1899

CC zero Frederic Eugene Ives 

Ives wanted to find a process to convert photographs into small black or white lines or dots, and to use a printing block which could be used alongside text blocks in an ordinary printing press. The lines and dots could vary in size, but had to be small enough that from a normal viewing distance they blended together giving the illusion of shades. 

The “Ives’ process” was gradually refined and photographs were rephotographed directly onto a metal plate coated with photoresist (a light sensitive material). The popularity of the process spread quickly and by the 1890’s it was used widely replacing earlier hand-engraved wood block and steel plate illustrations. This was the standard process for photographically illustrating books for the next eighty years.

3D view of the printing block at 200x magnification. Image shows the corner of the printing block showing the depth of the ridges/holes against a black background.
A 3D rendering and colour scale display of the Fairbairn printing block shows that the depth of the stippling is about 86 microns.
Colour scale display at 200x magnification, 3D visualisation using bright colours to indicate depth, against a black background.
3D visualiation of the halftone printing block. The dots are typically 86 microns in depth

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Electrolytic copper layer

Type metal (or hot metal) is the metal alloy used in typefounding and hot metal typesetting. It consists of mostly lead with some tin and antimony. The type metal in this block has a copper electrolytic layer and is screwed onto a wooden block. The electrolytic layer is very thin and can be scratched easily revealing the type metal underneath.

Close up of Electrolytic layer scratches at 100x magnification. Image shows orange surface with many scratches showing darker layer of metal beneath
Electrolytic layer scratches at 100x magnification
Image shows loss of electrolytic layer at 200x magnification. The metal layer below is visible and there are lots of visible scratches
Image of losses of electrolytic layer at 200x magnification

CC by The copper electrolytic layer is easily scratched. Areas of damage where the copper electrolytic layer has been lost reveal the type metal (lead with some tin and antimony) underneath

The printing block is backed with a paper sheet and ink stains pervade both the backing sheet and the wood block giving a wonderful insight into the history of the item. We often forget that collectibles which today gather dust were heavily used at some point in their lives.

Images shows microscopy of wood block which is standing on its side with the base towards us. The base is backed in paper and has many marks - evidence of its repeated use in the past.
Profile of the printing block under the microscope lens showing printer’s ink residue and paper backing under magnification
Image of block profile at 50x magnification. You can see the side of the block showing printers ink residue and the paper backing.
Image taken of the profile of the block at 50x magnification

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Halftones are considered to be what is known as a photomechanical or process print. Other photomechanical prints include line blocks, photogravures, photolithographs and collotypes. Digital halftoning replaced photographic halftoning in the 1970’s and the theory forms the basis for how the CMYK colour space works using dots of cyan, magenta, yellow and black. You can read more about CMYK in a previous @BL_CollCare post: What the CMYK? Colour spaces and printing.

The printing block in this article depicts Steve Fairbairn (1862-1938) and was kindly loaned by Pauline Churcher of Thames Rowing Club. The Head of the River Race is a 6.8 km processional rowing race held on the Thames each year from Chiswick to Putney with the tide. It was founded in 1926 by Steve Fairbairn who dedicated his life to the sport by both competing and coaching to high levels. The race began with 23 entries and today boats well over 400 crews. The coveted prize is a bronze cast bust of Steve Fairbairn - which is the image observed in the printing block.

Christina Duffy (@DuffyChristina), Imaging Scientist

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