Filed under: Art, Book Conservation, tech | Tags: blogging, book conservation, document conservation, framing, Gutenberg Bible, history, jim downey, Johannes Gutenberg, paper, parchment, technology, vellum, Wikipedia
I’ve previously mentioned that I do document conservation, such as a single leaf of the Gutenberg Bible. That item is paper, but one of the materials commonly used historically for important documents was parchment – an animal skin which is also called vellum. That was commonly used for grants of land or titles, affixed with one or more big wax seals. Such documents evolved over time, and the formal diplomas for college and graduate degrees you see today are their descendents — that’s why the term “sheepskin” is still used to refer to a diploma, because historically they were written/printed on actual sheepskin (or calfskin) parchment/vellum.
Parchment is still a wonderful material to write on, though it is expensive to produce and has one particular quality which needs to be taken into consideration: it is very hygroscopic — it reacts strongly to changes in humidity. Basically, when exposed to humidity that nice flat sheet of parchment wants to go back to being the shape of the animal it came from. So when it is used for a document you want to frame and display, that needs to be accommodated in some way.
Here’s one way it used to be done:
Yup, the parchment was just folded over a wood frame and nailed down.
But a rigid mount like that usually tears loose over time, like this:
To repair it, you have to slowly humidify the document in a controlled environment (without actually having it come in contact with liquid water), allow the skin to relax, then dry it under mild restraint. Usually a couple of cycles of doing that will result in a satisfactory return to “flat”, though to remove all the distortions can require many hours of labor — not typically what a client wants to do, unless the item is of great historical value. Here’s what the above item looks like after a couple of cycles of flattening:
Now it is ready for proper mounting and framing, using one of several possible framing treatments which will allow the document to ‘move’ due to changes in humidity without trying to rip itself apart.
But a lot of frame shops don’t know that they need to handle parchment/vellum documents a certain way. In fact, many places don’t know that there is such a thing as animal skin parchment/vellum … that’s because a century or so ago, paper manufacturers started to produce types of paper which supposedly had the same qualities for writing/printing as real parchment, and they called that paper “vegetable parchment”. It was a marketing ploy which worked entirely too well, to the point where people became confused about the differences between the two materials, and many people forgot (or never learned) that there was such a thing as animal skin parchment/vellum.
Now, when you have something printed on paper, and if that paper becomes distorted by humidity, one quick and easy way to flatten it is by ironing it. So long as it is done with a mild heat, and a brief exposure, it’s not *that* bad for most papers. After all, one of the ways modern paper is made is by running the sheets between heated rollers to dry and finish them. So if you take a document to a frame shop, and they find that document is a little warped/cockled, they may plug in the iron and see about flattening it.
But if you do that to animal skin parchment/vellum, it’s like cooking the skin. It doesn’t flatten out. It does this:
Sorry, that’s not a very good image. It’s what the client sent me via email*, asking if there was any hope for fixing it. I didn’t think to take my own ‘before’ image. I told the client that I wasn’t very hopeful, because heat damage can be permanent. But I agreed to try, and he brought it to me.
So I gave it the treatment outlined above, but with *very* slight restraint — I wanted to allow the skin to slowly try and relax. Here’s a pic after the first try:
You can already see improvement, even as bad as it still looks. That gave me hope that I could get the document mostly back into its original condition. The client asked me to try. Here it is after two more cycles of humidification and drying under restraint, using a little more pressure each time:
By no means perfect, but pretty good for a modest amount of labor. There’s always a trade-off with such work, between what is possible to do and what is reasonable to spend doing it. The client was very pleased with the result. So was I.
Just thought I’d share that.
*Since the diploma is a private document for a living person, I asked the client’s permission to use and display these images. That permission was kindly granted.
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