Earlier this year 144 fifteenth-century medieval miniatures from one of the Chester Beatty’s most treasured works, The Coëtivy Hours (CBL W 082), were re-mounted by the conservation team in preparation for the temporary exhibition, Miniature Masterpiece: The Coëtivy Hours (9th March – 2nd September 2018).
In general, the miniatures were in good condition and did not require any treatment prior to re-mounting, but one particular miniature, CBL W 082 f.295, required rather more care and attention.
An unsympathetic historic repair along the spine edge of the folio had caused the parchment to deteriorate and it was decided that conservation treatment would be beneficial, in order to improve the physical and chemical stability of the folio before it was mounted. For more information on the mounting process do take a look at our previous blog post here.
Four distinct areas of damage were visible along the spine edge of folio 295. It is likely that the losses may have occurred when the folio was removed from its binding, and could possibly correspond with the sewing stations of this previous structure. Unfortunately, when the damaged areas were repaired, the infill paper that was used was thicker, more yellow and several shades lighter than the original parchment, immediately detracting from the delicate illumination. When viewing the folio in transmitted light, it could be seen that the repair paper overlapped the parchment on both the recto and verso by 1-5mm. This overlap was not only visually displeasing, but also increased the risk of tensions occurring if the folio were to expand and contract in response to changes in relative humidity. In addition, the parchment along the repair edge had darkened and become embrittled, possibly due to aging of the adhesive with which the repair was applied.
For these reasons, it was decided that the historic repair and any residual adhesive should be removed, in order to prevent any further deterioration of the parchment support. Since parchment is very sensitive to moisture, mechanical removal of the repair was attempted in the first instance, but this was not successful. Instead, a small damp brush was used to introduce just enough moisture to swell the adhesive so that the repairs and adhesive could be carefully removed with a small dental tool.
As often occurs during conservation treatments, there was a stage where the object looked a lot worse than before the treatment began! As well as revealing the true extent of loss to the spine edge, removing the old repair revealed two small tears in the parchment. These were repaired on the verso of the folio using RK2 remoistenable tissue, prepared using isinglass (a proteinaceous adhesive derived from the swim bladder of sturgeon fish). Isinglass was chosen for its excellent ageing properties as well as its strong adhesion at low concentrations. It is also a collagen-based material, just like parchment. The prepared remoistenable tissue was cut to the desired shape and peeled off its Melinex backing. Then the repair paper was carefully positioned over the tear, activated with a damp brush and left to dry under a small weight. When dry, the two tear repairs were trimmed down and the folio was ready to be infilled.
The paper chosen for the infills was a Japanese sekishu paper (20 gsm), dyed with yasha (click here for more information on how this was prepared). The paper was thinner and lighter than the parchment, to ensure that it would work in harmony with the folio and avoid incurring any tensions between the two materials.
The folio was placed over a light box and a layer of Melinex was used as a barrier between the folio and the repair paper above. This allowed the shape of the first damaged area to be traced onto the repair paper with a water pen. A bamboo spatula was used to score along the same line and to tease away the remaining paper, revealing a feathered edge. Next, the edge of each infill was trimmed down with scissors and pasted with wheat starch paste. Over the light box, each infill was carefully positioned (with a 1mm overlap between the repair and the folio) and left to dry under light pressure. After treatment, the folio was mounted in the same way as the other miniatures and is currently on display in the Miniature Masterpiece: The Coëtivy Hours exhibition.
As an intern, this small project was a fantastic opportunity to learn more about parchment conservation. Discussing treatment options with the conservation team here at the Chester Beatty Library was an invaluable experience and I look forward to applying what I have learnt to new parchment projects in the future.
Alice Derham, Conservation Intern
A lavishly illustrated catalogue by exhibition curator Dr Jill Unkel (Curator of the Western Collection), with contributions from Dr Laura Cleaver (Ussher Lecturer in Medieval Art at Trinity College Dublin), and our own Kristine Rose-Beers (Senior Book Conservator), is available from the Library’s gift shop for anyone who wants to have an even closer look at the brilliance of this miniature masterpiece.