Matting was originally developed as a method of protecting artwork by isolating the surface of the artwork from the surface of the glass, as well as away from the edge of the wood frame.
This is important because the glass tends to condense moisture and provide an ideal environment for mold to grow on the surface of the artwork. Also, wood becomes increasingly acidic over a period of time and acid migration can occur to the artwork. It was some time after its functional invention that the decorative qualities of matting seemed to overcome the original purpose. If a mat is considered undesirable for whatever reason, some means of separating the surface of the artwork from the surface of the glass is still necessary. Setting the artwork back away from the glass can be accomplished by using a wood or plastic spacer of approximately 1/4 inch along the frame between the backing and the glass.
In setback framing, I mount the backing board to the support board, because I have seen too many backing boards creep out from the edge of the setback material. This happens because of mishandling or the natural expansion and con-traction that these boards may undergo with changes in humidity. Particularly with setback framing, contemporary galleries often frame with wooden support bars built into the back of the picture frame for added strength.
This is often necessary for frames that are large and/or will be handled a great deal. Support bars are a particularly good idea when glazing with clear acrylic sheeting in larger sizes because plastic sheeting tends to bow and can pop out of a picture frame.
The following rules apply to most paper, fabric, and any work that needs to be protected from the atmosphere and mechanical abuse.
1. Never mount permanently any valuable or potentially valuable artwork, unless the artwork requires the support, such as a collage or a piece of artwork that cannot support its own weight. If it cannot be held in two places without risk of tearing or distortion, it should be considered for mounting. If you do choose to mount, you should regard the artwork and the mounting board as one piece permanently.
The definition of conservation mounting seems to be undergoing some revision. The old definition is that the adhesive should be pH neutral, water reversible, and of vegetable origin. The original reason behind the use of vegetable-based adhesive was that other pastes were of animal origin and tended to become acidic as they aged as well as less reversible with water. The pH neutrality is important because acidity breaks down cellulose and weakens the paper. If there are lignins (the natural glues that hold plant cells together) still present in the paper, the paper will turn brown. Acidity can also affect many dyes and pigments dramatically by changing their colors. Recent studies show that an adhesive may appear to be pH neutral to start with, but that there are no guarantees it will remain so over many years. Reversibility with water was important to conservators because the adhesive could easily be washed out without damaging the artwork. Today, however, a large variety of materials may be used to pro-duce a piece of artwork. There are many pieces that would be destroyed or seriously altered if washed in water but would not be if washed in other solvents. Finally, there are now chemical adhesives that indicate the possibility of aging characteristics equivalent to vegetable-origin adhesives.
So, you may ask, “What do I do?” If you must mount the picture, decide which will affect your artwork the least—water or organic solvents. Watercolors, for example, would be affected less by organic solvents, while etchings would be less affected by water, if removal of the artwork from the support became necessary in the future. Select an adhesive that has a good record for nonyellowing and for maintaining pH neutrality over time, and that will be least harmful to your artwork if you have to remove it.
2. Never use pressure sensitive tapes, such as masking, drafting, magic, surgical, and packing tapes. All these tapes will self-destruct and severely damage artwork wherever it is touched by the tape. There are currently only two exceptions to this rule—tapes produced under the name Filmoplast by Hans Neschen GmbH & Company in Germany and Archival Aids Document Repair Tape made by Ademco Products in England.
3. Never secure artwork in more than two places. Exceptions to this rule should be made only with extremely wide pieces and with the understanding that for every additional place the artwork is secured you risk having twice the number of ripples. This is because the natural expansion and contraction of paper from variations in temperature and humidity will be restricted. Recommended methods for securing artwork will be discussed later.
4. Never use any ground-wood pulp-board or paper, chipboard, or cardboard as backing or storage for artwork. These boards, especially corrugated card-board and chipboard, are highly acidic, contain iron and copper, and have been known to damage artwork, even without direct contact. The acids can even bleed through four-ply museum boards.
5. Never use conventional wood pulp boards for matting or backing of original or valuable artwork. Instead, use museum or conservation boards. Unless the boards are of 100 percent rag or are of lignin-free alpha wood pulp that has been buffered to remain acid-free, they will damage the artwork. Such damage can be seem as soon as six months, and may in some cases be irreversible. Pulp boards may be used only if they are not in direct contact with the artwork and are separated by a four-ply museum or conservation board. With matting, the edge of museum board should extend at least 1/4 inch past the edge of the wood-pulp board to prevent any acids in the wood-pulp board from cascading over the edge of the museum board.
6. Never use single-strength glass larger than 36″ x 48″. If you have not already guessed the reasoning behind this rule, you should first consult an insurance agent regarding the extent of your insurance coverage.
7. Never glaze with acrylic sheeting for artwork done in charcoals and/or pastels. Plastic sheeting can develop a powerful static electrical charge and can lift a significant amount of material off the paper on to the plastic surface. You should also be aware of the fire hazards of plastic sheeting and its ability to give off poisonous gases when burning with insufficient oxygen.
8. Never put original or valuable artwork, especially glossy photographs and acrylic paintings, in direct contact with the glass in a picture frame. Glass tends to collect moisture on its surface, and when it comes in contact with the surface of paper artwork it can provide an ideal environment for the growth of mold. Foxing, which is the appearance of small brown spots on artwork, is most often attributed to mold. However, foxing can also be caused by iron deposits in reprocessed wood-pulp backing boards. Photographs and acrylic paints, primarily due to the nature of their surface films, tend to adhere to glass over a period of time and the surface of the artwork can be damaged if the picture has to be removed.
9. Never allow the edges of a piece of artwork to touch the edge of a wood frame. Wood has lignin, which breaks down and becomes acidic. Moreover, many woods, such as oak, are naturally highly acidic. The artwork should be at least inch away from the edge of the wood.
10. Never cut, trim, or in any way alter an original piece of artwork without the clear consent of the owner. In California, it is a violation of the law even for the owner to alter a recognized piece of artwork without the consent of the artist! California passed the Art Preservation Act of 1979, which was amended in 1982 and became the model for similar acts in New York and Massachusetts. The law provides for actual and punitive damages as well as attorneys’ fees for willful disfigurement or destruction of fine artwork.
11. Leave restoration to a recognized professional restorer. Most professional restorers spend a great deal of their time correcting the work of self-appointed amateurs.
(Excerpt from ART HARDWARE: The Definitive Guide to Artists’ Materials, by Steven Saitzyk © 1987)