Parchment repair

The repair and mending of parchment has taken place for thousands of years. Methods from the earliest hand stiching of tears to today's use of modern equipment to mend and fill parchment show the importance we have placed on its preservation and conservation.

Properties of parchment

In order to repair parchment it is important to know not only how it is made but also what it is made of. To make parchment, animal skins are soaked in water, covered in a lime solution, rinsed off and relimed. These limed skins are made up almost entirely of collagen fibers which consist of long chains of amino acids. The wet skins are dried under tension and scraped to remove the hair from the surface. This causes the alignment of the fiber network of the skin to be in a pattern more parallel to the surface of the skin. (Reed 1975)

In parchments, the chemical bonds between the amino acid chains help maintain the fiber structure and typically render it insoluble in cold water (Woods 1995). The collagen fibers exhibit a sudden shrinkage when heated in water (Haines 1987). Parchment is generally hydrophilic; it "soaks up water rapidly and wet parchment has poor resistance to micro-organisms...but greater resistance if kept dry." (Hansen, Lee, Sobel 1992)

While collagen is insoluble in cold water, the amino acids in parchment which has been limed will dissolve in boiling water and go into a gelatin solution. While the proper relative humidity needs to be maintained to preserve parchment, water can have many negative affects on parchment as a consequence of its method of production.

Water has a strong surface tension so as a wet skin dries, the water is lost from between the fibers and the surface tension draws the fibers together. During parchment production the tension applied to the wet skins maintains the space between the fibers while the water dries out. The correct amount of tension to the limed skin is critical in parchment manufacturing but it can make it undesirable to wet parchment during conservation because if the same amount of tension is not used it will alter the parchment being repaired (Woods 1995).

Methods of repairing parchment

Flattening and crease removal
While wetting parchment can cause damage sometimes it is necessary. If it is a problem of access then minimal humidification might be needed. Today there are also a number of methods used to repair parchment, some using little or no water.

One method to use if the entire piece of parchment needs to be flattened is to lift the relative humidity by using a gentle heat source to warm a small amount of water in a humidity chamber. Once the relative humidity(RH) of >95% is reached the heat source is turned off and the parchment is added. The amount of water used is based upon the size and weight of the parchment. One important factor to monitor according to Bety Haines' is to make sure the vapor has penetrated to the core uniformly, and at its own rate, and not just the surface of the parchment. Once this has happened the use of tensioning with clips will allow creases to be eased.

If just a few creases need to be eased to access information you can use a mixture of iso-propanol and water at a 90% or 80% alcohol to 10% to 20% water ratio. (heavier skins might need the higher water content)

This mixture is azeotropic, which according to Chris Woods, means "that the alcohol will not evaporate away leaving all of the water behind. The water is evenly dispersed in the alcohol and, although some humidity is left behind, the vast majority of the solution evaporates together as a mixture." The solution also has a lower surface tension than water so the fibers suffer less shrinkage. The solution can be applied with a Q-tip and then gently pulled flat by hand.

Another method of localized treatment is the use of an ultrasonic water mist which adds humidification in a controlled area. During the process tension is gradually placed on the edges of the parchment to release the creases and then it is dried under pressure between polyester web and thick wool felts.

Cleaning
Any surface dirt should be removed before humidification which can cause the dirt to become ingrained and might make it impossible to be removed at a later time.

Mending tears
Examples of early mending techniques were often as basic as hand stitching the tear together. Today adhesive-coated tissues and animal membranes are used for repairing splits and tears.

The adhesive chosen for parchment mending is important so as not to further damage the item being repaired. Using adhesives with the least amount of moisture needed to perform the repair will most likely have the most positive effect on the parchment.

Since parchment is mostly collagen and collagen boiled in water becomes gelatin, a gelatin solution (although pure, without lime)can be used for parchment repair. Gelatin has similar ageing characteristics and is somewhat hydrophilic, The solution used is typically 12% powdered gelatin added to 88% water and warmed to 80 Celsius while stirring continuously (Woods 1995). According to Anthony Cains there should also be added three drops of 2% aqueous sorbitol (as a humecant) and two drops of an aqueous solution of 1% acetic acid (to aid the effectiveness of the adhesive)for every 100 ml of solution. These replace the honey and vinegar that were added in earlier days.

Before use the solution should be heated to 100Celsius for 5-10 minutes which will give it a higher degree of tackiness. For application to the parchment the solution must be cooled but still liquid. The adhesive should be applied to the repair material and not directly to the parchment as it can turn it transparent is too warm.

Suggestions for the actual repair materials vary. Many recommend the use of Goldbeater's skin which is the appendix of calf intestine. Others use light-weight, long-fiber Japanese tissue.

In cases where a minimal amount of water can come in contact with the parchment a process described by Tatyana Petukhove, a paper conservator at Cornell University Library, can be tried. Isinglass, similar to animal gelatin, is a dried film that can be reactivated with ethanol and water. It is made by soaking and then cooking a dried Russian sturgeon bladder at low temperature. Honey or a few drops of glycerin are then added. Isinglass is known for its adhesive strength and used with tissue.

Infilling of Losses
When parchment has ragged edged holes or is missing whole areas then more extensive repairs will need to be made to strengthen it. This process is called infilling and uses a pulp mixture to fill in the missing areas.

In a treatment used in 1985 by Per Laursen, a Dutch conservator, "the parchment ...is laid on a paper suction table and a dry powder, made from unprocessed animal hide, is applied to the area of loss with a spray apparatus. The excess hide powder is brushed away from the surrounding area and the fill is lightly sprayed with ethanol and smoothed in place through a piece of polyethylene. A casein-based adhesive....is applied with a brush to the dry powder fill, which is left to dry for about 10 minutes."

The parchment will then be dried between polyester web with blotters under pressure for 12 hours. The problems with this treatment are that the fill is not always even in thickness and large areas have trouble adhering and need to be supported on both sides with goldbeater's skin.

In Hungary a pulp was also made from untanned animal hide but ground up with it were Japanese paper (for color) and a sulfite-processed paper pulp.Parchment size incorporating wine vinegar, hydroxyethylmethylcellulose, ethanol, isopropanol and a fungicide were also added to the mixture. The parchment is placed on a suction table with a light box underneath and the pulp applied with an eye dropper. The fill will be applied to both sides of the parchment if needed.

Another fill method applies the pulp to a piece of silk which is later lifted off and pressed gently into place on the parchment. This method introduces less moisture to the parchment.

Problems with past conservation methods

Parchment is very durable and many pieces have lasted hundreds of years, often with little help. Sometimes the "help" from conservation methods in the past has caused more damage than good.

Based on the properties of parchment it is obvious that the addition of water can cause quite a bit of damage. Water has typically been used to flatten parchment to make its information more accessible and to allow for the ease of further repairs such as mending with starch paste. Paste also can cause problems.

Starch paste is a low-tack (not overly sticky when wet) glucose-based carbohydrate. the parchment is often moistened by the paste but typically just the area where the paste is applied so when the paste dries there is a humidity imbalance in the parchment that results in a distortion around the paste. This distortion irreversibly affects the skin structure.

According to Woods, "starch cannot be considered compatible with parchment., My understanding of campatibility is the use of like with like...The principle is that if genuine, damage-free reversibility is not possible, it may be better to use the same material as that of which the conserved item is constituted, since its aging characteristics are known to be sympathetic." Instead of using starch paste which is a glucose carbohydrate that is not hydrophilic, it would be better to use something which is protein based and hydrophilic.

Parchment preservation ethics

There are many ethical issues when working with parchment manuscripts. One of these issues is whether or not to add any toning to pulp to color it or to use colored Japanese papers for mending. The concern is that the repair should be easily recognizable as a repair and not try to look like the original parchment. Some conservators feel though that some color is desirable as it reduces the brightness of the new materials.

References

Abt, Jeffrey; Fusco, Margaret. (1989) A Byzantine Scholar's Letter on the Preparation of Manuscript Vellum, "Journal of the American Institute for Conservation", Vol. 28, No. 2, pp. 61-66.
Quandt, Abigail B. (1996) Recent Developments in the Conservation of Parchment Manuscripts, "The American Institute for Conservation Book and Parer Group Annual", http://aic.stanford.edu/sg/bpg/annual/v15/bp15-14.html
Woods, Chris. (1995) Conservation Treatments for Parchment Documents, "Journal of the Society of Archivists", Vo. 16, Issue 2, pp 221-239.
Wachter, Otto. (1962) The Restoration of the "Vienna Dioscorides", "Studies in Conservation", Vol. 7, No. 1, pp. 22-26.
Hansen, Eric F., Lee, Steve N., Sobel, Harry. (1992) The Effects of Relative Humidity on Some Physical Properties of Modern Vellum: Implications for the Optimum Relative Humidity for the Display and Storage of Parchment. "Journal of the American Institute for Conservation", Vol. 31, No. 3, pp. 325-342.
Cains, A. (1983) Repair Treatments for Vellum Manuscripts, "The Paper Conservator", Vol. 7, pp. 16-17.
Reed, Ronald. (1975) The Nature and Making of Parchment. United Kingdom, Leeds; Lemete Press.