Collection Care blog

Behind the scenes with our conservators and scientists

4 posts from February 2014

23 February 2014

‘No pigments were harmed in the making of this post’

Conservator Joanna Blackburn reports on the conservation of a large collection of botanical watercolours.

When I was at school, chemistry was not my favourite subject. My young mind hadn’t quite made the connection yet between the inexplicable results I would get from my experiments, and the world I saw around me. So when I decided to become a conservator, imagine my horror when I realised I would have to take a course called ‘Chemistry for Conservators’!

I needn’t have worried though, because I found science so much more interesting when applied in context. And there is nothing more satisfying than looking at the deterioration of a collection item and being able to explain the ‘whys’, the ‘hows’ and the ‘what nexts’.

Below is an example of one of a large collection of botanical watercolours that my colleague, Patricia, and I have been working on over the past six months.

NHD 54 Item47

CC by NHD 54 item 47

The collection comprises of 309 watercolours by Chinese artists, dated to around 1800. Their exact provenance is unknown, but they would have been commissioned by a Western traveller to bring back to Europe. They would have fuelled the popular interest in botany of the time. The collection was received by the Library from the Foreign and Commonwealth Office in 1975. The watercolours are not unusual in British collections, many institutes have similar examples, but the reason ours is special is because the format they arrived in has remained almost untouched. They were inserted loose into volumes of simple quarter leather case style binding with plain cloth sides. Interestingly though they are sewn on three vellum supports which are still good even if the leather and sewing is not.

NHD 52

CC by NHD 52 - Simple quarter leather case style binding with plain cloth sides

This housing has done a marvellous job of protecting these vivid and exotic watercolours. The vibrancy of the colours has been preserved by lack of light exposure, and the paper is in fine condition. Many of the drawings had little Chinese character labels attached with pins, none of which have been lost, or caused damage to the paper!


CC by Detail of NHD 53 item 8, example of pins used to attach small labels to many of the watercolours.

In the following image, you can see a close up of the green pigment used to paint many of the leaves of the botanical specimens.

NHD 54 detail

CC by NHD 54 - Detail of typical damage seen in green pigment areas

As you can see, the pigment layer has cracked and is erupting into a tent shape along those cracks. So why is this happening to the green when all the other colours are happily bonded to the paper? As you can see from the shiny appearance of the leaf, it appears to have been varnished. This was done with a number of the watercolours to deepen the green of the leaves and to recreate their smooth, waxy texture. Such a beautiful effect has had unfortunate consequences, creating a rigid glassy surface, which is unforgiving if the paper substrate is flexed or expands in humid environments, leading to detachment and cracking of the pigment layer.

So what next? Consolidation of pigments is one of the most challenging treatments carried out by conservators. It is usually done through a microscope because the flakes tend to be extremely small, and it is crucial to choose the right consolidant for the materials involved. Several factors must be considered. Is there a risk that the consolidant will alter the surface appearance? What viscosity does it need to be to be effective? What long term impact will it have on the collection item? After considering all these factors we chose a traditional Japanese adhesive obtained from algae, called JunFunori.

Another reaction that has occurred during the lifetime of these items is the transformation of the white pigment, lead white (basic lead carbonate), to lead sulphide. This chemical reaction occurs in the presence of pollutants such as hydrogen sulphide and sulphur dioxide, and results in greying of the white areas. The petals that you see in the image below are tipped with that grey hue, which is the colour of lead sulphide.

NHD 54 Item28

CC by NHD 54 item 28 - An example of ‘blackened’ lead white, a pigment which turns into lead sulphide in the presence of pollutants

There are ways that the conservator can counteract this often unsightly reaction, but it is not a decision taken lightly. The treatment, which involves the use of ethereal hydrogen peroxide, does not turn the compound back into its original state. It changes it, once again, into lead sulphate, a more stable compound.

So the dilemma for the conservator is to balance their duty to preserve the aesthetic value of an object as well as the integrity of the materials that it is formed of. Each case must be considered on an individual basis, and at the Library we have yet to be presented with an item whose criteria justifies this particular treatment. So, these drawings will keep their funny little grey patches as evidence of the materials their creators chose.

NHD 53

CC by The finished article! NHD 53 item 1 in its volume after conservation

This beautiful collection is a prime example of how important it is for conservators to treat these heritage items with a light hand; retaining material in the format it comes to us wherever possible. This involves difficult decisions, and almost every project presents its own dilemmas. And that’s exactly why we do it!

Joanna Blackburn, Patricia Tena and Royston Haward

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'.

10 February 2014

The Colour Red

The colour red has long been associated with seduction, sexuality and love. It is the colour we use to symbolise the heart, and the colour most in our minds on Valentine's week. Take a moment out from the important work of colouring in your Valentine's cards with red crayons to appreciate the colour itself. Forget about wooing with poems - what could be more romantic than sharing some facts about the colour red?

Additional MS 35166 f. 8v.

Figure 1: February 14th: The apocalypse is coming. Surprise your loved ones with a beautiful bunch of hand-picked flames. Additional MS 35166 f. 8v.

Pigments and dyes are colourants which have been used throughout history on wall murals, ceilings, paintings, illuminated manuscripts and textile materials. The difference between pigments and dyes is that pigments are insoluble (resulting in a suspension), while a dye is either itself a liquid, or is soluble (resulting in a solution). 

Red ochre

The colour of red ochre comes from the mineral hematite, or iron ore. Red ochre has been found in prehistoric cave paintings and is believed to be the first pigment used by man.

Altamira Bison painted on the cave walls at Altamira, Spain.

Figure 2: Red ochre used on a painting of a bison in the cave of Altamira, Spain, dating between 15,000 and 16,500 BC.


The colour of vermilion comes from the mineral cinnabar which is the ore of mercury. It was used in Roman times and sourced from mines in Almadén in Spain. Due to the highly toxic nature of mercury, many of the miners (who were usually prisoners or slaves) died from poisoning. Vermilion pigment has been found on wall murals in Pompeii and on Chinese lacquerware dating to the beginning of the Song Dynasty.


Figure 3: Vermilion pigment made from cinnabar.

Madder red

Madder red comes from the roots of Rubia tinctorum, a yellow greenish flower. This dye was the most common red dye used until the nineteenth century. The first synthetic red dye, called alizarin, was created by German chemists in 1868 to duplicate the red colour of the madder plant.


Figure 4: The relative cheap production and long-lasting nature of Alizarin meant dyes from the madder plant significantly declined in production.

Red lead

Red lead, or minium, (chemically known as lead tetroxide) has been used since the ancient Greeks. It was prepared by the Romans by roasting lead white pigment. Its use was common and is observed on some illuminated manuscripts at the British Library.

Red lead

Figure 5: Red lead is found on initials in some gospel manuscripts to heighten the significance of the text. Image attribution: BXXXD at the German language Wikipedia.

Lake pigments

Lake pigments are pigments manufactured from a dye by precipitating the soluble dye with an inert binder, usually a metallic salt. Red lac (red lake, crimson lake, carmine lake) is a lake pigment used widely in Renaissance and Baroque art. A red sinuous substance secreted by scale insects, called gum lac, was used to make red lac. Carmine lake is made from crushed cochineal insects. This anthropod feeds on the sap of live oak trees and is native to Mexico and South America. Red lake pigments were translucent, and so thin layers had to be built up on paintings. Due to their organic dye composition, lake pigments become unstable and faded when exposed to sunlight.

The Vendramin Family Venerating a Relic of the True Cross.

Figure 6: Red lac used by artist Titian, oil on canvas 1540-1545: The Vendramin Family Venerating a Relic of the True Cross.


We see many examples of the colour red in manuscripts at the British Library. During the times of medieval manuscript production scribes known as rubricators (from the Latin rubric “to colour red”) were responsible for enhancing manuscripts already laid out and written by another scribe. Rubricators would add titles, chapter headings or instructions not strictly part of the text, but as an aid to separate out components. These additions were known as rubics which can also refer to the red ink or pigment used. Notes in the margins are often seen on manuscripts instructing rubricators where to add the red text.

Harley MS 2367, f. 70v showing rubrication.

Figure 7: Rubrication in BL Harley MS 2367, f. 70v.

Harley MS 2893, f. 93v showing black ink and rubrications.

Figure 8: Rubrication in BL Harley MS 2893, f. 93v.

There will undoubtedly be many amateur rubricators in action this week, so take some inspiration from the professionals by perusing the Digitised Manuscripts website.

Christina Duffy (@DuffyChristina)

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

CC zero 

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