Nicholas Pickwoad: The Lanhydrock Pedigree: mounting and framing an oversize parchment document

The Lanhydrock Pedigree was completed for Sir Richard Robarts of Lanhydrock in Cornwall in 1620, and remains in the house, which now belongs to the National Trust. It is a very large document written and drawn on six skins of calf parchment joined with glued overlapping joins measuring overall approximately 2270mm x 1230mm. The skins are arranged in two columns, that on the right consisting of three large skins placed horizontally (with the animal spines running horizontally), and that on the left consisting of three smaller skins arranged vertically, and the animal spines probably also running vertically. There is text written in an iron gall ink and the rest is picked out in a wide variety of colours and shell gold.

The pedigree was hung in a glazed frame, probably dating from the mid-twentieth century, but was previously, as is evidenced by the green ribbon tie attached to the leader at the head of the document, kept rolled. The document was not secured in the frame, but simply sandwiched between the glass and the hardboard backing board, and it would appear that after framing, the document expanded in the humid conditions in the house, a process which further exacerbated the cockling.

It was clear from the lack of register in the drawn lines at the overlapping joins that the pedigree had been in pieces at some stage and was reassembled with additional strips of parchment to reinforce the joins glued to the verso. The sheep parchment leader was presumably also added at the time of these repairs – perhaps in the nineteenth century. The repairs and the contrary spine direction of the skins had resulted in extensive cockling, some of it fixed in place by the glued joins. There was also a long, vertical and ragged crease in the centre of the document, the result of rolling the document when it was cockled.

The National Trust wished to keep the pedigree on long term display, but the existing frame and mounting were clearly inadequate for this purpose and were contributing to its continuing deterioration. The fact that it had once been in pieces and had lost the original register of lines crossing the joins made its disassembly for treatment an uncontroversial option. The leader and the parchment strips (and the glue securing them) were removed and sheets separated. Once separated, the skins were surface-cleaned with plastic eraser and the pigment checked for stability and consolidated as necessary. The cleaned skins were then relaxed in a humidification chamber and allowed to dry under tension to reduce the cockling, after which the whole document was re-assembled. The added leader was not re-attached, but preserved separately. This work was carried out by Nicholas Hadgraft. The re-assembled document was then rolled up to reduce the risk of further distortion while a decision was made about how and where to display it. The decision was finally made in 2011 to display it on its own in a purpose-built frame in a small room in which other documents relating to the family were also to be shown.

Parchment documents of this size present considerable challenges in terms of mounting and display, especially over the long term, as relatively modest changes in RH levels can result in significant changes in dimension, added to which the different spine directions in the different skins could well set up new tensions which would result in further cockling and distortion unless the document could be held under light tension. The question was how to hold such a document under tension within a frame. The thread-mat technique pioneered by Christopher Clarkson in which the threads extend beyond the piece o parchment to more than double its width and height was clearly not going to work on something of this size. The best answer was to mount the document on springs, which would allow it to expand and contract and keep it under slight tension within a climate-controlled frame.

The design of the frame and mounting system was the result of a close collaboration with Stuart Welch and Robert Campbell of Conservation by Design, who produced a wall-mounted frame made from black powder-coated aluminium extrusions with an inner track that held adjustable metal tabs with a hole at the inner end to take one end of the stainless steel extension springs, the other ends of which were hooked through brass eyelets in new parchment tabs which were glued with parchment size to edge of the back of the document.

The frame is hinged on one side to allow access to a compartment in the back of the sealed capsule (which is lined with Charcoal felt) to hold a Prosorb cassette conditioned to 50%RH), and glazed with 6mm Truvue Optium Museum Acrylic in a hinged door sealed with a silicone sponge gasket, which can be opened to allow access to the document for installation and maintenance. There is a temperature and humidity probe located inside the frame connected to a wall mounted transmitter with a display of relative humidity and temperature. The document is held by 46 tabs and springs on each side and 29 each at head and tail. The springs across the top are powerful enough (Tension rate 9.3 N/mm) to be essentially solid, and are intended to take the weight of the document, but those on each side are quite weak (Tension rate 0.07 N/mm), to provide a light, evenly distributed tension. Within 30 minutes of being mounted on the springs, the slight cockling in the document was visibly reduced, and a year after installation, the document remains in good shape.