For years there have been assorted techniques promoted for the mounting of 'sheepskins' and generally there is more than one way to skin a cat. But in order to better understand the positives and negatives of attempting to mount parchment we need to first examine the origin and differences of this tricky animal.
The use of vellum animal skins for recording history has long been an accepted practice, and skins have survived from as early as Egypt 2500 BC. Calf, goat and sheep were normally used, but skins of gazelle, antelope, stag and ostrich have been uncovered and preserved. Vellum is the proper name given for any high quality animal skin excluding sheep or lamb. Though all writing skins are often referred to as 'parchment', the only true parchment comes from sheep.
In ancient times the preparation of skins for writing was crude. Archbishop Hildeberg of Tours in the 11th century tells that prior to writing on skin the scribe cleaned remains of fat and other impurities with a razor then pumiced it with a stone to smooth and remove tendon lines. On the other hand, it was said that Cicero had an extensive library of parchment in which there existed a parchment so fine that the whole story of The Iliad was written upon it and fitted into a nutshell.
Parchment is Sheepskin
Genuine sheepskin parchment is used for printing, writing and bookbinding whenever excellence or distinction is desired. This is the reason many ivy league universities continue to produce diplomas on original sheepskin instead of artificial parchment or fine grade printing paper.
The skins from sheep are whiter and oilier than vellum. To prepare them sheepskins are first pickled for storage then in large batches are depickled, scraped, limed, then finally squeezed to remove moisture. Skins are then tied to a wooden frame at 21 points around the edge of the skin, and allowed to dry 5-6 days. The skins are then scraped (for the second and third times), degreased, shaved, pumiced, purified, and whitened, all by hand. Then they are set aside to dry slowly to ensure a flat even skin. Dried skins are cut from the wooden frame for finishing and/or cutting into smaller pieces.
Though the process for preparing vellum is similar to sheepskin, while sheepskins are sorted and selected after dewooling, calfskins and goatskins are selected prior to dehairing. After the hair has been removed, there is a long liming process lasting up to four weeks. Shaving of vellums takes much longer and is more difficult, requiring much greater skill for it is easy to remove too much or too little of the skin reducing its value.
New skins are generally stored rolled and reverse rolling will lie them flat. Most vellums are sold as whole skins unlike sheepskin parchment which is also available in rectangular shapes. Vellums are generally creamy in color and often showcase the veining of the animal, while parchment is whiter and has a much smoother surface. Unlike paper, the preparation of natural animal skin cannot be mechanized.
Parchment and Vellum Today
Though the use of animal skins appears to be more limited to university diplomas in the United States, in other parts of the world it is extensively used for everything from wedding invitations to royal proclamations (photo 1). Skins are sought after for their longevity because of their complete lack of acidity due to the cleaning and purification processes. No two skins are truly alike. This in turn is part of their natural beauty and the basis for framing them true to their nature...unmounted. Fully mounting a piece of parchment or vellum using any process restricts it from the natural expansion and contraction it craves through variations in relative humidity. Preservationally, a skin document or diploma should be hinged or conservationally mounted. If a document is slightly buckled it is the nature of the beast and is truly a part of the total effect and appearance, it should be allowed to thrive.
This 1852 sheepskin parchment ledger sheet has been encouraged to curl through the application of tolerable heat (180°F), but excessive pressure.
Flattening for Conservation Handling
If a cracked, wrinkled, or rolled document has been brought in and needs to be made flat, the best advice for the framer is to be very careful about offering to mount it at all. Moistening and flattening procedures on this type of project often should be contracted to a book or paper conservator in your area. Relaxing and flattening a badly damaged document may involve soaking in water then slowly drying between Pellon and blotters beneath a weight. If it has become dry and brittle forcing it flat could crack it.
There are many areas that require testing prior to submerging any skin document, such as testing for ink and paint permanence, or wax seals. Also skins will react differently depending upon what animal they are but more so how they were prepared for use in the first place.
For help in locating a conservator in your area contact the American Institute for the Conservation of Historical and Artistic Works, 1400 16th Street NW, Suite 340, Washington, D.C. 20036.
Flattening with Moisture and Pressure
Since vellums are originally dried on frames much like stretcher bars, when dampened they will cockle and warp, and attempt to revert to the original shape of the animal as they dry (if left to dry under no restraints). So to reflatten vellum, it must be dampened and dried under tension or pressure, such as plate glass weights (photo 2). But even flattened skins will buckle again with increased relative moisture.
This 5x7" vellum sample was first soaked in distilled water then allowed to freely air dry under no pressure, encouraging it to cockle (lower right corner). Left side was then pressed flat at 160ºF using a mechanical press. The top portion was then dry mounted to 4ply mat board using BufferMount tissue at 165ºF for 3 minutes and cooled under a glass weight.
Simple flattening of a slightly cockled or warped piece is very easy to do by a framer. Skins may be redampened to relax them in an attempt to reflatten prior to framing. Tests should still be done on the document prior to dampening to determine the permanence of the inks and pigments used. With a dampened Q-tip, touch each individual color lightly to check for bleeding or lifting of color.
A humidifier is a great way to moisten a document. A makeshift humidifier may be made with two plastic garbage tanks, the larger one having a lid. Place the smaller in the larger and surround it with a moat of water, keep the smaller inner one dry. Place the document in the dry tub and close the lid. It will relax as it absorbs the moisture in the tank.
Heavily dampening parchment will both effect the surface finish and may shrink the skin, about 5% overall (photo 3). To lessen these dramatic effects, use the lightly dampened blotter method by pressing it to the skin for just a few seconds. Then press the parchment between clean, dry blotters, placing a sheet of Pellon between the skin and the blotter, under even weight like that of a closed (not locked) cold mechanical press or piece of plate glass large enough to cover the entire piece.
The left sample illustrates a piece of sheepskin that has been dampened and air-dried. There is about 5% natural shrinkage due to the original stretched cleaning process. The right sample shows the unfortunate damage resulting in applying both moisture and heat to the parchment at the same time.
A 50/50 solution of alcohol and distilled water may also be used during the dampening process, and dampening may be done from the back of the document with a cotton ball, squeezed sponge, or mist bottle. Another version is transferring moisture into the skin by moistening a blotter and then placing it in contact with the back of the skin, but be careful this can bond to the document if left too long.
Change the blotters every ½ hour if very soaked, 4 hours if misted, until completely dry. Do not leave damp blotters in contact for extended periods to the skin as it promotes mold growth. Most skins will water stain (some worse than others) so spot dampening should always be avoided and parchment will definitely want to curl.
Parchment is much more delicate than vellum and reacts much more violently when mishandled. Predictability is the key, always know what will happen prior to doing anything. Many applications (ie: moisture and heat) individually are quite safe, but when applied in collaboration can be deadly to that "one-of-a-kind" sheepskin ledger page from 1852 (again, photo 3).
If You Must Mount
Occasionally the customer will dogmatically announce they want it flat, regardless of its natural tendency to buckle through moisture expansion. Although mounting is often possible, it should be discouraged. These are often one of a kind collectibles or originals and should be treated as such. Documents, certificates and diplomas should be treated in the same manner as a fine art original. Museum mounting using all the standard conservation methods of hinging with wheat starch and Japanese hinges on only acid-free 4-ply boards should always be stressed. Slight buckling of a skin with natural temperature and humidity changes truly is the nature of the beast.
Other options for mounting depending on the skins include: stretching over coated bars or acid-free museum board and affixing to the back; wet mounting with adhesives specified for skins; and dry mounting. Additional heat applications involve Lamin-all (a heat setting wet glue) and Parchweld. Both of these last two methods involves a combination of taping, heat and pressure. Even when vellum is stretched like canvas it will cockle as time passes and the natural effects of the above mentioned temperature and humidity tighten and relax it. Of course the ideal environment is 60-70F with 50% relative humidity.
But if the plunge is taken and the risks are all understood, then often parchment may be mounted using many methods. None will be preservation, or reversible. When a dogmatic client pursues the more static and flat look, dry mounting fully dried skins with low temperature, removable, acid-free tissues is quite simple and effectively successful. Acceptable dry mount tissues include BufferMount, TM-4, Drychival or Acid Free Mounting Adhesive.
Vellum will notoriously tolerate much greater temperature and moisture abuse than parchment. Applying heat alone to skins will not radically effect them as long as it is not too hot. Tests show that temperatures of 180ºF for up to 5 minutes will not do damage to either vellum or parchment samples, although a tendency toward brittleness does begin to occur. High temperatures of over 200ºF will be asking for trouble, for parchment could literally be fried, it is a real skin. Care should always be taken when applying heat of any kind, though 160ºF for 3 minutes to set any low temperature tissue is very safe (photo 2, sheepskin onto BufferMount).
A combination of heat and pressure while damp will slightly shrink most vellum (almost undetectably), while it may do major damage to parchment (photo 3). Make certain any skin having been dampened to flatten is totally dry and clean of all other adhesives prior to mounting to avoid any irreversible damage. Use your common sense, vellum and parchment are both natural animal skins and will readily react to other natural elements safely, when adding extremes of heat (an unnatural element) the other elements need to be totally under control.
Both stretched and mounted versions of presentation are unnatural to vellum and parchment, for it assumes an inconsistent character from the true natural look. If archivally hinged, skins should be placed ⅛" from the glazing for room to breathe, which can easily be achieved by using multiple neutral pH window mats (this pressure against the edges of the vellum will also minimize overall buckling. Once framed these pieces of fine art should be hung in a dry location, preferably out of direct sunlight. Taken well care of, these archivally preserved masterpieces will last many future generations.
Copyright © 1999 Chris A Paschke
For more articles on mounting basics look under the mounting section in Articles by Subject.
Additional information on all types of mounting is found in:
The Mounting and Laminating Handbook, Second Edition, 2002,
The Mounting And Laminating Handbook, Third Edition, 2008 and
Creative Mounting, Wrapping, And Laminating, 2000 will teach you everything you need to know about getting the most from your dry mount equipment and materials as an innovative frame designer.
All books are available from Designs Ink Publishing through this website.
Chris A Paschke, CPF GCF
Designs Ink Publishing
785 Tucker Road, Suite G-183
Tehachapi, CA 93561