10 September 2013
Is not parchment made of sheepskins? Ay, my lord, and of calfskins too...
Hamlet (Act V, Scene I), William Shakespeare
Parchment and vellum
Parchment is an animal pelt, most often sheep, calf, or goatskin, which has been unhaired by liming or enzymatic action and then stretched on a frame while wet. This stretching and drying under tension causes the collagen fibres in the dermal layer to be realigned resulting in a thin, opaque membrane. Most commonly used as a writing substrate, parchment is also used as a covering for bookbindings and to make drumheads, among other things.
Named for the ancient city of Pergamum, where the manufacturing technique is believed to have been developed around the 2nd century BCE, parchment was the principal substrate for writing in Europe throughout the Middle Ages until it was gradually superseded by paper, which could be manufactured more cheaply and in greater quantity. Parchment has persisted, however, remaining popular for official documents and presentation copies. Indeed, you might be surprised to learn that UK Acts of Parliament are still printed on parchment today and it was even used for the marriage certificate of the Duke and Duchess of Cambridge!
What of vellum?
Though the terms parchment and vellum are often used interchangeably, strictly speaking vellum is parchment made from calfskin (from the Old French vélin, meaning calf). Vellum can also be used to describe parchment of superior fineness or quality.
Some of the most important Treasures of the British Library, including the Lindisfarne Gospels (left) and the Magna Carta (right) are written on parchment and vellum.
The Lyte Pedigree
The Lyte Pedigree, (BL Additional MS 48343) c.1605, is a manuscript copy of the royal genealogy in iron gall ink on parchment. It is the work of the genealogist Thomas Lyte, who also wrote Britianes Monarchie, a manuscript tracing the ancestry of King James I (BL Add. MS 59741). The Pedigree is one of two copies of the royal genealogy prepared by Lyte for James I. The other, an illuminated copy on paper presented to the King in 1610, is no longer extant.
Originally a rectangle comprising nine parchment skins, the genealogy is now a cruciform shape comprising five skins, with the four corner skins having been lost. The genealogy is over two metres wide and almost two meters high.
The Lyte Pedigree first came to the Centre for Conservation in spring 2012 in order to be prepared for loan to the British Museum for the exhibition, Shakespeare: Staging the World, which opened in July 2012.
For storage the two side panels had been folded in and the document had been rolled. This, combined with heavy parchment repairs over the joints on the verso, had resulted in extensive creasing and cockling and meant that the genealogy would not lie flat, as it was intended to be displayed in the exhibition.
The genealogy was opened in the studio and the heavy joining strips on the verso were removed, as were some old silk gauze repairs on the recto. A number of temporary repairs were carried out using Japanese paper and wheatstarch paste and the genealogy was left open to relax under light weight for several weeks. It was recommended that a more appropriate storage solution be found once the genealogy returned from the exhibition.
Since the genealogy is comprised of five individual animal skins, each has unique tensions and stresses. The use of newer parchment for repairs had exacerbated the tension resulting in extensive cockling and creasing. This, combined with the rolled storage, meant that the genealogy was difficult to handle and vulnerable to damage during consultation.
Following consultation with the curators, it was agreed that upon return from the exhibition, the five skins would be separated and individually mounted. Not only would this be more conducive to the long term preservation of the genealogy, it would also allow for easier handling and facilitate consultation. It was proposed that the skins be flush-mounted, which would enable the genealogy to be exhibited as a whole by placing each skin adjacent to the next in its original position.
Parchment is a very hygroscopic material as it can easily absorb moisture from the air and is very vulnerable to rapid changes in humidity. Aged parchment is particularly vulnerable due to the breakdown of the collagen fibres over time. Too much moisture can result in gelatinisation and complete loss of structural integrity. As a result any conservation treatment on parchment must minimise the use of water. Humidification is carried out rarely and always in a minimal, slow, and controlled manner.
Once the five skins had been separated from each other they were first allowed to acclimatise to the atmosphere in the studio under a light weight for a number of weeks.
After careful deliberation, it was decided that in this case, due to the severity of the cockling and creasing, gentle humidification would be necessary. A combination of techniques was used. First, two of the most cockled skins were humidified in a cedarwood chamber, raising the humidity to 70% RH for several hours. The cedarwood chamber was lined with damp capillary matting, followed by a layer of Gore-Tex, which allows water vapour (but not liquid water) to pass through it. The document was then placed in the chamber on a sheet of Bondina, a humidity meter is placed inside, and a Perspex sheet placed on top, sealing the chamber. Second, local humidification using a cold ultrasonic mist was applied to sharp creases in the two side panels where they had been folded in for rolling. After humidification the parchment was dried under tension using magnets.
As the parchment gradually relaxed and the cockling reduced, some of the remaining old parchment repairs began to lift and cause greater tension. It was decided that they should be removed and new repairs were made using remoistenable Japanese paper. Losses were built up using layers of paper, toned to blend with the parchment. Remoistenable tissue has been pre-coated with a thin layer of adhesive (in this case Isinglass) which can then be reactivated using a minimal amount of moisture. It is used for repairs when it is necessary to keep moisture to a minimum, such as in parchment conservation and when repairing documents with iron gall ink or fugitive media.
Following conservation, the individual parchment skins were mounted on corrugated board using tabs of Japanese paper. Narrow tabs (10mm) were spaced at 30mm intervals to ensure even tension across the skin. The weight of the paper was carefully chosen to be weaker than the parchment so that in the event the parchment were to move, the paper tabs (and not the parchment) would tear.
Tabs of Japanese paper were adhered to the verso, overlapping the edge by 2-3mm, using dry wheatstarch paste (left). These were wrapped around archival corrugated board (cut to the size of the parchment) and pasted on the verso of the board (right).
Finally, each mounted skin was placed in a Plastazote recess to compensate for the natural undulations in the parchment and prevent abrasion of the surface, then housed in a phase box. Plastazote is a chemically inert polyethylene foam commonly used for conservation enclosures.
Clarkson, C. (1992) Rediscovering Parchment: The Nature of the Beast. In: The Paper Conservator, Vol. 16 (1), pp. 5-26.
Reed, R. (1972) Ancient Skins, Parchments and Leathers. London: Seminar Press.
Mariluz Beltran de Guevara
Conservation Team Leader / Specialist in the conservation of vellum and parchment.