When matting paper artifacts, using the right materials is essential. Paperboards for mounting must be chemically stable with good aging properties. These are the so-called archival-quality, or acid-free, boards sold by conservation suppliers. They are free of lignin and are pH neutral or, more often, slightly alkaline. It is also important to choose the methods and materials for attaching the artifact to the mount are also important. The traditional method is to hinge the object with Japanese paper and a starch paste. More recently, corner supports or edge strips have come into favor since these can be used without applying adhesives to the object.
A window mat is the customary mount for a work of art or valuable artifact on paper. A mat is composed of a top sheet with a window and a backboard (see Figure 1). The two boards are held together with a strip of cloth tape along one edge, usually the top. The window permits the object to be seen while the mat protects it from handling and isolates it from surrounding materials.
In the past, museum-quality mats for works of art were expected to be made of rag fibers, that is, cotton or linen. Today ragboard is still favored by museums, but some lignin-free, wood-derived boards are now accepted by the preservation community. Mat boards of either type are usually buffered with an alkaline material to neutralize any acids they may absorb as they age. It is important to confirm the quality of the board with the supplier and by reading descriptive material provided by the manufacturer.
Four-ply board is the thickness most often used for matting. Larger works of art or those with undulations or raised elements such as seals may require a thicker board for the window portion of the mat. Boards heavier than four-ply are available from conservation suppliers, or they can be made by laminating two or more four-ply boards. Sink mats may also be used (see Figure 3). These are constructed by adhering strips of conservation board to the backboard to make a recess, or "sink," in which the object is mounted. The sink construction is hidden by the window portion of the mat.
Mats can be ordered from any framer, but making them yourself can save money. The tricky part is learning to make a neatly cut window opening, which is usually beveled (cut on a slant). This is best learned by practicing with an experienced technician. With practice, a skilled person can make a beveled window with a simple utility knife, but a mat cutting device greatly simplifies the procedure. There are a number of mat cutters on the market. The best of these are the easiest for an inexperienced person to use. Such mat cutters are expensive but will pay for themselves if cutting mats is to be an ongoing activity.
Hinging is the customary way to mount an object in a window mat. The artwork is hinged, usually with Japanese paper and starch paste, to the backboard of the mat, never to the reverse of the window. This keeps an object stationery when a mat is opened and avoids potential damage from encountering an object attached where it is not normally expected to be. As shown in Figures 1 and 2, part of the hinge is attached to the object and part to the backboard. Hinges allow the artwork to be removed easily from the board if that becomes necessary. Under no circumstances should the object be adhered directly to the mount. Alternatives to hinging are suggested toward the end of this leaflet.
High-quality Japanese papers, sometimes referred to as mulberry papers, make effective hinges because they are strong without being bulky and do not discolor or weaken with age. Traditionally these papers were made by hand, but now Japan exports machine-made papers of suitable quality. They are available in different weights and under a variety of names. The names are not specific and do not guarantee the fiber content of the paper. Some Japanese papers contain wood pulp and are not appropriate for conservation purposes. To be safe, use sheets made of 100 percent kozo fibers and buy them from conservation suppliers, not general art or paper suppliers.
Hinges should have torn edges. Tracing an incised line in the paper with a wet artist’s brush allows you to pull the paper apart to create an evenly fibrous edge. A torn edge creates a less obvious hinge attachment, especially on thin or transparent papers.
Figures 1 and 2 show two common types of hinges. Folded hinges (Figure 1) are tucked out of sight under the object. They must be used when the object is “floated,” i.e., when the edges of the artwork are visible within the window. Pendant hinges (Figure 2) use two pieces of paper that form a T. The bottom of the T is adhered to the reverse of the object. The top is attached to the backboard, often with a cross piece for added security.
Hinges are usually placed at the top edge of the work of art. If the object is small, a hinge at each upper corner provides adequate support. Larger objects or those on heavy paper require additional hinges evenly spaced along the top edge. If the object is to be floated, additional hinges at the bottom corners or along the edges are desirable. Large sheets that tend to curl may require several small hinges on each edge if they are 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. If the mat covers the edges of the object, thereby helping to hold it in place, fewer hinges are needed. Hinges should be small, less than three inches across. The part of the hinge that is adhered to the object should extend less than 1/2 inch into the sheet. Use several small hinges rather then a few large ones. Large hinges or a strip across the top edge may restrict the natural movement of the paper in response to environmental fluctuations and encourage rippling.
Adhesives for hinging must have three qualities that remain constant over time:
Few, if any, commercially available adhesives meet all these criteria. Staining from self-adhering tapes and from adhesives such as rubber cement and animal glue is frequently seen by conservators. There are commercial adhesives that do not stain, but these usually are not permanent or easily reversible. The “archival” self-adhesive tapes sold by conservation suppliers are probably more stable than other commercial products. However, because their aging properties are not yet known and conservators usually have to resort to organic solvents to detach them, they are not recommended at this time for objects of value.
Conservators recommend starch paste or methyl cellulose. The paste is homemade from pure starch extracted from flour, usually wheat or rice flour. This starch is available from conservation supplier vendors. A recipe for starch paste follows, as well as directions for making paste in a microwave oven.
Because refrigeration may cause the paste to lose its tack, keep it at room temperature. It is best to make small batches, since the paste does not usually keep for more than a week. A preservative can be added, but these chemicals are toxic and not recommended.
University Products, a supplier of conservation materials, publishes a quick, easy paste recipe in its catalog. This is ideal if paste is used only occasionally and in small quantities. Strain and dilute the paste beofre use, as above.
Place 1 tablespoon of wheat starch in a clean, microwave-safe container, add 5 tablespoons of distilled water, stir, and place the mixture in a microwave oven. Microwave on a high setting 20 to 30 seconds, remove the paste, and stir. Place it back in the unit and microwave it another 20 to 30 seconds. Remove it and stir again. Repeat 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 be cooled to room temperature before it is strained and diluted for use.
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 and does not need to be cooked. Add 1 rounded tablespoon of methyl cellulose powder to 1/2 cup distilled water, stir, and let stand for several hours. Thin to the consistency of mayonnaise with distilled water. Methyl cellulose absorbs water slowly so dilution takes a few minutes. Methyl cellulose is not as strong as starch paste but should give adequate support for objects of moderate size. It keeps for several weeks and does not require refrigeration.
Before hinging, assemble the following:
It may take time before hinging comes easily, but practice pays off.
In recent years some institutions have been reluctant to apply adhesives to artifacts, especially if they are valuable. Mounting without adhesives can be done with corner supports or edge strips.
Small corners of chemically stable plastic (polyester film) or archival paper are commercially available for mounting photographs. Although photo corners work well for many photographs and for small works on paper, they are too small to support larger objects. Larger envelope corners (made from folded paper) or strips across the corners give better support, but they cannot be hidden under the mat unless the object has wide margins.
Hugh Phibbs, coordinator of matting and framing services at the National Gallery of Art in Washington, D.C., has developed innovative ways of mounting without adhesives. Generally speaking, these methods involve supporting the object on the mat with strips of archival-quality paper that are folded over the edges of the object to hold it in place. The strips are adhered to the backboard at their extremities. Phibbs gives workshops periodically, and his ideas appear in a monthly column in Picture Framing Magazine. Some of these articles are cited below.
Munro, Susan Nash. "Window Mats for Paper Objects." Washington: National Park Service Conserve O Gram 13,1:(1993).
Phibbs, Hugh. "Preservation Matting for Works of Art on Paper." A Supplement to Picture Framing Magazine (Feb. 1997).
__. "Reinforcements for Support Strips." Picture Framing Magazine (Jan. 1998).
___. "Stable Support for Overmatted Artwork." Picture Framing Magazine (Dec. 1997).
Smith, Merrily A. Matting and Hinging of Works of Art on Paper. Washington, D.C.:Library of Congress, 1981.