REPAIRING PAPER ARTIFACTS

REPAIRING PAPER ARTIFACTS
by Sherelyn Ogden
Preservation Consultant and Conservator
St. Paul, MN

The generally accepted method of repairing torn paper or reinforcing weak areas in a sheet uses strips of strong, almost transparent, acid-free paper, adhered with a strong, colorless water-based adhesive that is acid-free and easily reversed. The following materials are recommended for repair of documents, book pages, and other paper objects.

The preferred repair papers are made in Japan from kozo fibers. These papers (often erroneously called rice papers) exist in different weights with names such as Sekishu, Tengujo, Kizukishi, and Usumino. The fiber content of Japanese papers differs, with some papers containing fibers that are not of conservation quality. To be safe, only papers that contain 100 kozo, mitsumata, or gampi fibers, or a combination of these, should be used. These Japanese papers are ideal for repairs because they do not discolor or become brittle over time, they have long, strong, flexible fibers, which produce a lasting repair. The lighter-weight papers are especially well suited to the repair of documents since they are translucent and unobtrusive and will not obscure the text of a document. Most conservators use strips of paper with torn rather man cut edges because a frayed edge makes a less visible, softer repair.

ADHESIVES
Use of a proper adhesive is essential. Any adhesive used for mending paper objects must have the following properties:
-Sufficient strength: it should hold the object for an indefinite length of time.
-No tendency to discolor: it should not yellow, darken, or stain.
-Reversibility: it should allow the repair paper to be easily removed with minimal effort and no damage to the object, even after many years.
-Few commercially available adhesives meet all these criteria. Commercial library and wallpaper pastes may lose hold as they age and often contain harmful additives. Rubber cement and animal glues usually darken or stain. Several synthetic adhesives, such as white "glues," are very difficult if not impossible to remove once they have begun to age.
-Pressure-sensitive (self-adhering) tapes should be avoided. Most of the adhesives on these tapes cause staining over time and require toxic solvents and technical expertise for removal. In recent years pressure-sensitive tapes that are advertised as archival have been introduced. These are probably more stable than other similar tapes but because their aging properties are not yet known, their use should be avoided for objects of value. The adhesives on commercial gummed tapes, which require wetting, are less damaging, but most stain in time and these tapes also should be avoided for objects of value.
-Commercial products in general should be avoided even if they are reputed to be safe because commercial products are subject to alteration by the manufacturer. This year's non-staining tape may have an adhesive with a different formula next year.

Starch-Based Paste
For many years conservators have favored homemade starch-based pastes. These are made most often from either rice starch or wheat starch (not flour, but the starch that has been extracted from the flour). There are many recipes for these pastes. One recipe for wheat starch paste follows:
1. Place one part of wheat starch and four parts of distilled water in a saucepan or the top of a very clean double boiler.
2. Mix well and let stand at least 20 minutes.
3. If a double boiler is used, fill the bottom part with a small amount of water making sure that the upper section does not touch the water.
4. Place on medium high heat and cook, stirring constantly with a clean wire whisk.
5. When the paste begins to thicken (this may happen right away), reduce heat and continue stirring. Stir for about half an hour; then remove from the stove. The paste should be thick and translucent. As it cooks and thickens, it will become more difficult to stir. To aid in stirring, a wooden spoon may be substituted for the wire whisk, but the spoon should be one that has not been used for the preparation of food.
6. When cooked, the paste should be transferred to a clean container for storage. It should be allowed to cool before use. Prior to use the paste should be strained. A Japanese paste strainer works well for this.

Quick Wheat Paste
University Products, a supplier of conservation materials, has published a quick recipe for wheat starch pastel. The advantage of this recipe is that small quantities of paste can be easily prepared- If necessary strain the paste prior to use.
Place 1 tablespoon wheat starch in a microwave-safe container, add 5 tablespoons distilled water and place in microwave unit. Microwave on high setting 20 to 30 seconds. Remove paste and stir. Place back in unit and microwave another 20 to 30 seconds. Remove and stir again. Continue this process several times until the paste is stiff and translucent. If larger quantities are made in the microwave oven, increase the cooking time between stirrings. Paste should cool before use.

Diluting and Storing Paste
Different consistencies of paste are required, depending upon the particular mending task at hand. A consistency similar to heavy cream is adequate for most mending. Pastes should be diluted with distilled water to achieve the consistency required.
Starch paste should not be refrigerated; cover and store in a cool, dry place. It will keep for only a week or less. Some conservators recommend adding a preservative. The preservatives used, however, are toxic. It is preferable to make paste in small quantities when it is needed rather than add a preservative and store it for long periods. If paste discolors, grows mold, or develops a sour smell, discard it immediately. Discard it if dark flecks appear in the paste since they may indicate mold or bacterial growth.

Methyl Cellulose
Starch pastes require time to make and thus are not practical if they are to be used only occasionally. A simpler adhesive can be made from methyl cellulose, which comes in powdered form and is sold by viscosity (in general, the higher the viscosity the more stable the methyl cellulose). Mix one rounded tablespoon of methyl cellulose with 1/2 cup of distilled water. Let it stand for several hours before use. It will thicken on standing but can be thinned to me appropriate consistency with water. Methyl cellulose is not as strong as starch paste but should hold adequately if the document is not to be handled extensively or if it is to be encapsulated in polyester film. Methyl cellulose keeps well for several weeks and does not require a preservative.

MENDING PROCEDURES
Tearing Mending Strips
It is desirable for mends to have a soft edge, both to increase the strength of the bond and to prevent paper from breaking where it bends against the edge of the mend. To tear mending strips, draw parallel lines of clean water on the Japanese paper using a small, soft artist's brush, a ruling pen filled with water (instead of ink), or a small cotton swab. Tease the mending paper apart along the wet lines. Make the strips different widths to conform to different tears; 1/4", 1/2", and 3/4" will be most useful. If many mends are to be made, it is helpful to tear a supply of strips m advance.

Applying the Mending Strips
Using a flat piece of glass or plastic as a pasting surface, apply starch paste or methylcellulose to a strip of Japanese paper with a Hat brush (about 1/4" wide). Include the exposed fibers on &e edges of the strip. Then lift the strip with tweezers and place it over the tear. If the document is one sided, then mend on the reverse, with the pasted side against the document. Lighter-weight papers tend to pull apart when wet with paste. For this reason it is easiest to use strips not more than two inches long. For longer tears, several short strips may be used, placed end to end. It will take practice to manipulate the thin, wet repair strips. Once the mending strip is in place, lay a sheet of silicone release paper or non-woven polyester (Reemay, Hollytex) over the repair. Tap the repair lightly.

Drying the Mended Sheet
If possible, weight the repair while it dries. Weighting insures good adhesion and prevents cockling of the paper. Repairs may be weighted as follows: first place small pieces of release paper or non-woven polyester over and under the area to be dried. Sandwich these and the mend between pieces of blotter. Lay a piece of glass on top of the sandwich and put a weight (about one pound) on top of the glass. The weights may be small bags of lead shot or pieces of lead covered with cloth. One pound fishing weights from sporting good stores make excellent weights provided they have at least one flat side to prevent rolling. Repairs should be weighted for one hour or longer. A photographer's tacking iron, placed on a low to medium setting, can be used to speed up the drying process- The tacking iron should not be applied directly to the document. Place a piece of non-woven polyester between the iron and the document- Iron until dry (10 to 20 seconds) then weight for a few minutes to flatten.