Repairing parchment with collagen

Christine Hughes, through Jonathan S. Farley
<j.s.farley<-a t->lib< . >hull< . >ac< . >uk>, writes

>At Hull City Archive Office we are currently researching the
>history, background, and use of collagen as a repair material
>for parchment.

A few years ago I repaired a Bugatti rocking chair that was
parchment or vellum stretched on a frame, with some painted details.
The skin was split in the center of the front of the back (it was a
fully wrapped frame--the back of the chair had a front and back
skin), apparently from storage in a heated but not humidified
warehouse. I built a plastic work tent and put in a humidifier,
increasing the humidity over a period of one month until the skin
was completely relaxed. I then used sausage skin (from Faicco's) for
the repair, using an adhesive made from boiled down vellum, PVA
(Elvace 1874), and flour paste. I tried all sorts of things
individually and in combination, but this was the only combo that
worked on this with correct properties when dry.

I was surprised that the flour paste helped. I needed a specific
combination of tack, slip and drying time, and the repair had to
move with the skin (same coefficient of expansion) relative to
temperature and humidity, so it wouldn't pucker or split later. It
also had to have the same optical properties, as the skin was
translucent.

The skin needed to be sanded from behind to reduce the thickness in
the repair area so the patch wouldn't be obnoxious when light passed
through it. When the repair was complete I reduced the humidity over
a one month period until it had equalized with the room, and advised
the client to be careful in the future about storage conditions.

If anybody comes across this chair, please let me know how well the
repair has held up.

Richard

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                  Conservation DistList Instance 10:89
                 Distributed: Thursday, April 17, 1997
                       Message Id: cdl-10-89-006
                                  ***