One of the major purposes of framing is to diminish or delay the effects of aging on artwork. This means protecting the art from damage arising from:
- physical abuse like bumps, punctures, abrasion, and dirt
- the chemical effects of air pollution
- excessive light
- excessive heat or cold
- excessive humidity or dryness
Young artists generally pay little attention to the quality of materials and the future of their work, but as we get older we try to ensure that we use "artist quality" materials in our work. These are materials such as pigments and papers that will not deteriorate over time. Nonetheless very few artists succeed in using these materials all the time; most don't have enough money to do so, and many contemporary artists work spontaneously in unconventional media, grabbing anything at hand and including it in their work. In addition, I have found that not all materials labeled "artist grade" are in fact lightfast (no fading). Therefore people who buy original works of art should not assume that the work is going to last "forever" (why should it? nothing else does), but should instead consult with the artist and framer, and use common sense in considering the materials used and how to best preserve them for a reasonable cost.
Framing to fully preserve the art is often called "museum" framing, but museums must preserve art for all time, while most of us need to preserve it only for a lifetime or two. Museum framing has a very stringent sent of protocols that demands, among other things, the full reversibility of anything done to the art. The framing discussed here might better be called "preservation" or "acid-free" or "acid-reducing" framing, which is similar but less stringent, and allows for some irreversible procedures, such as mounting with non-resoluble adhesives. I will also focus on works on paper, since the vast majority of my own work is on paper.
Preservation framing has become increasingly important because of the increasing acidity of papers and pollution of the atmosphere. Most papers are made from wood fibers and are more or less acidic, and, upon exposure to acids in the air or acids in objects placed near them, become even more acidic and turn brown and brittle. The "cheaper" the paper, the quicker this happens; everyone knows a newspaper turns dark and brittle very quickly. At the other end of the spectrum are "acid-free" paper products, either made of non-wood plant fibers like cotton or linen (hence called "rag") or of alkali-buffered wood pulp. Using these products in producing, framing, and storage will preserve the art for the longest possible time.
The framer can help primarily by surrounding the artwork -- front, back, and sides -- with acid-free materials. One purpose of the mat, for example, is to provide a three-inch buffer between the art and pollutants that creep in from the edges. Of course the mat itself should be acid-free. When acidic mats are put in contact with the art paper, acid migrates from the mat and creates visible browning of the art paper, not just directly under the mat but also creeping into the art from the edge of the mat. This may be noticeable around the edge of the mat widow within a year or so, and damages the fresh, pristine look of the art.
Of course, the art paper should also not come into contact with acidic materials from behind; never put corrugated or grey cardboard up against the back of a valuable work of art. Foam boards are not usually completely acid free, but they are quite inert and, except for the most valuable or delicate pieces, are probably adequate for backings. But don't mount valuable art onto foam board; it is too easily dented and punctured.
Frequently compromises are made (not by museums, but by the rest of us). For example, less expensive, acidic materials may be used inside the frame, but not right next to the art. This is okay, if done correctly, and may prevent visible damage for many years, but keep in mind that it is the acidity of the entire environment within the frame that will ultimately affect both the art paper and media.
If you want to preserve works on paper for many decades, then, you should use acid-free mats and backings. But this is expensive, so be reasonable. If you have an inexpensive, replaceable poster, or a crayon drawing with fugitive colors that will fade in a year, there's no point in trying to make the paper last a century. The good news is that the life span of even very acidic paper can be greatly lengthened by acid-free framing, especially by mounting it to acid-free backing, because then the acids actually migrate OUT of the paper, although the paper will still gradually darken. If you don't mind the darkening, even works on newsprint will last just fine if properly cared for.