A Technical Leaflet from the Northeast Document Conservation Center
The importance of using proper materials for matting and mounting works of art on paper is becoming a matter of increasing concern to the informed public. Archival-quality, pH neutral (acid-free) mat board in different shades of white and a variety of colors is now available from conservation suppliers. These boards are stocked by an increasing number of framers to meet the demands of a preservation-conscious public. This public is also aware that the methods and materials used for attaching paper objects to the appropriate mounts are as important as the mounts themselves.
The standard mount for a work of art on paper is a mat composed of a window and a back board (see Figure 1). The two boards are held together with a strip of cloth tape along one edge, usually the top. Once matted, an object is ready for framing or storage in a drawer or box. The function of the window is to permit the art to be seen while insuring that nothing potentially harmful is in direct contact with the object.
Mats for works of art have traditionally been made of all-rag cotton fibers. It is important to confirm the quality of the board by asking the supplier and reading descriptive material provided by the manufacturer. Use only 100% cotton or linen “rag” or boards described as “low lignin” or “lig-free.” Today many boards are buffered with an alkaline material to insure that the board will not become acidic as it ages. Four-ply board is most commonly used for matting. Larger works of art or those with raised elements may require the use of a thicker board for the window portion of the mat. Thicker boards are available from conservation suppliers or they can be made by laminating two or more four-ply boards.
Matting and hinging can be done inhouse. With practice, a skilled person can cut a mat window with a simple utility knife, but using a mat cutter simplifies the procedure. A number of such devices are on the market. A good cutter is expensive but will soon pay for itself if mat cutting is to be an ongoing activity.
The work of art is attached to the back board of the mat with paper hinges and a chemically neutral adhesive which should be permanent, non-staining and reversible. Hinges are small tabs of strong, archival-quality paper. Part of each hinge is attached to the object being mounted and part to the back board. Hinges are used because they allow the art work to be removed easily from the board should the necessity arise. The object should never be adhered directly to the mount nor should it be attached to the back of the window portion of the mat. Two different types of hinges are shown in Figures 1 and 2.
Papers for Hinging
Japanese papers, sometimes referred to as mulberry papers, are used for hinging because they are strong without being bulky. The best Japanese papers for hinging are those made of 100% kozo fibers, which are especially strong and chemically stable. These papers do not discolor or become brittle with age.
Traditionally they were handmade, but conservation suppliers are now importing machine made papers of comparable quality from Japan.
Japanese papers are available in different weights and a variety of names such as Koro, Okawara, Sekishu and Kitukishi. The fiber content of these papers differs; some contain wood pulp and are not of conservation quality. To be safe, buy only sheets known to contain 100% kozo fibers. The paper can be cut or torn to make the hinges. When hinging thin or transparent papers a torn edge may create a less visible attachment.
Placement, Size and Number of Hinges
Hinges are usually placed at the top edge of the work of art. If the object is small and the mat covers its edges, thereby holding the object in place, a hinge at each upper corner will provide adequate support. Larger objects or those on heavy paper will require one or more additional hinges evenly spaced along the top edge. If the object is to be “floated” (shown with the edges exposed) additional hinges at the bottom corners are desirable. Papers that tend to ripple may require several small hinges on each edge if they are to be floated.
The number and size of the hinges as well as the weight of the hinge paper depend on the weight and size of the object being mounted. Hinges should be small. They rarely need to be wider than three inches, Very large hinges or a strip across the top of the object may restrict the natural movement of the paper and encourage rippling.
Types of Hinges
Figures 1 and 2 show two commonly used types of hinges. Folded hinges (Figure 1) are tucked under the object and must be used when the edges of the work are exposed. Pendant or tab hinges (Figure 2) are not folded. Tab hinges often use two pieces of Japanese paper to form a “T”. The stem of the “T” is adhered to the reverse of the object being mounted. The cross of the “T” is attached to the back board. This cross piece may be either Japanese paper or a commercial archival tape. Do not use archival tape for folded hinges.
Envelope corners are another method of attachment that can be used with small objects and photographs. To make an envelope corner a piece of archival-quality paper is folded over the corner of the picture and adhered to the back board behind the object.
No adhesive touches the work of art. Corners made from chemically stable plastic (polyester film) are commercially available and are acceptable for mounting photographs.
Adhesives for Hinges
Use of a proper adhesive is essential. Any adhesive applied to a work of art on paper must have three qualities that remain constant over time:
1. Strength. It must hold for an indefinite period.
2. Permanent color. It should not yellow or darken.
3. Reversibility. It must allow the hinge to be easily removed with a minimal amount of moisture, even after several years.
Few commercially available adhesives meet all these criteria. The staining properties of most self-adhering tapes and adhesives such as rubber cement and animal glue are well known. Unfortunate evidence of their use is frequently encountered by conservators. There are commercial adhesives that do not stain but are neither permanent nor easily reversible. Several “archival” tapes and adhesives have entered the market in recent years. While these appear more stable than other commercial products, their use has not yet stood the test of time.
Conservators recommend paste made from pure starch. This starch is extracted from wheat or rice flour and is available from conservation suppliers in powdered form. A recipe for a wheat starch paste follows .
Wheat Starch Paste
1. Place one cup of wheat starch and five or six cups of distilled water in the top of a clean double boiler.
2. Mix well and let stand at least 20 minutes.
3. Fill bottom part of double boiler with a small amount of cold water so 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 paste begins to thicken (which may happen immediately), reduce heat and continue stirring.
6. Stir for about half an hour; then remove from stove. The paste should be thick and translucent.
As it cools and thickens, it will be more difficult to stir and a wooden spoon may be substituted for the wire whisk. The spoon should be one that has not been used in the preparation of food.
7. Transfer paste to a clean jar or covered glass container and allow to cool. If a fungicide is to be used, (always with proper precautions), now is the time to add it to the paste (see below). Paste must be cool before it can be used.
8. The paste, which becomes hard and rubbery when it cools, must be strained and thinned before it is used. Strain a small amount of the paste through cheese cloth or a Japanese paste strainer (available from conservation suppliers).
9. Slowly mix the strained paste with cool distilled water until the paste reaches the consistency of mayonnaise.
This wheat starch paste should not be refrigerated. It is best to mix small batches, since the paste will not usually keep for more than a week. While a preservative can be added, these are toxic and are nor recommended for home use.
Quick Wheat Paste. University Products, a supplier of conservation materials, has published a quick recipe for wheat starch paste. The advantage of this recipe is that small quantities of paste can be easily prepared. If necessary strain the paste prior to use.
Place [I T.] wheat starch in a deep container, add [5 T.] 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 for 3 to 4 minutes depending on the power of your microwave unit. Paste should stand for a few minutes after microwaving before use.
Another Simple Paste: Methyl Cellulose
Methyl cellulose, the main ingredient in most commercial wallpaper pastes, is acceptable for conservation purposes if used in its pure form. It is available from conservation suppliers as a white powder. Mix one rounded tablespoon of methyl cellulose powder with 1/2 cup distilled water and let stand for several hours. Thin to the appropriate consistency with distilled water. Methyl cellulose is not so strong as starch paste but should give adequate support for objects of moderate size. Methyl cellulose paste keeps for several weeks and does not require a preservative or refrigeration.
Apply starch paste or methyl cellulose to one side of the hinge with a small stiff brush before the hinge is put in place. Cover the hinge with a thin layer of paste. Position the hinge, using tweezers if necessary, and tamp it lightly with a small piece of blotting paper. Weight the hinge as it dries to prevent cockling of the object. Hinges may be weighted as follows: place a blotter over the area to be dried. Place a small piece of glass over this with a weight of at least one pound on top. Small bags of lead shot or lead fishing weights from a sporting goods store are excellent. The hinge should be weighted until it is dry. Changing the blotting paper occasionally will speed up the process.
Folded hinges will sometimes stick together as they dry. one way to prevent this is to insert a piece of household waxed paper between the two parts of the hinge. Conservators use release paper or polyester web (available from conservation suppliers).
It may take time before hinging comes easily, but persistence and practice will pay off.