Matting
There are 4 basic considerations in choosing matting: color, size, design and the level of conservation quality required. The following is a breakdown of the types of boards available:

Types of Mats

Wood Pulp Base Mats (also referred to as "paper mats") - Paper mat boards contain lignin, the resinous material in wood which eventually breaks down and creates acids. Over time, these acids will "burn" the artwork, making it discolored and brittle. Humidity will accelerate this reaction, and over time the acid migrates into the artwork. This can be seen most distinctly on older prints which have been in the same frame for a period of time; the artwork turns brown and becomes brittle, with the area along the mat's sight edge turning the darkest.
Paper mats are often buffered with calcium carbonate, which can also be found in antacid tablets. However, this simply slows the process. Paper mats are the least expensive option on the market.
Uses: We recommend that paper mats only be used on posters or mass produced prints that are of lesser value and are not printed on acid-free paper.

Buffered Acid-Free Matboards - These are matboards that have had most of the lignin or acid removed during manufacturing and a buffering agent added. Buffered boards can also be matboards made with 100% rag with a colored facing paper on it. The reason for the colored facing paper is to offer more color choices than are available in pure rag boards (more on those below). The facing paper is made from alpha pulp, which is wood pulp which has had the acid removed. Wood pulp mats that are labeled "buffered" by the manufacturer have calcium carbonate added to neutralize the acids. However, over time the buffering agent loses its efficacy, therefore these types of boards should not be considered for artwork that requires the highest level of conservation quality.
Uses: Buffered matboards that have had most of the lignin removed are good for those who need conservation quality mat board but who desire colors beyond the neutral palette of most pure rag boards.

Alpha Cellulose Boards - These are made of pure cellulose and are free from harmful lignin. These are sometimes called "conservation boards" and from a PH standpoint they remain stable over time. In that sense they are considered equivalent to 100% rag boards.

100% Rag Mat - These are solid color boards (no colored facing paper) manufactured from pure cotton that has been rendered to a pulp. They are lignin-free and non-acidic; however, many cotton rag mats have calcium carbonate added to buffer any acidic materials that might migrate into the frame package. Some photographs are printed with emulsions that are sensitive to calcium carbonate (alkaline). For these, there are calcium carbonate-free rag mats, sometimes referred to by manufacturers as "photo rag mats."
Rag mats are the highest quality of conservation mat board, though colors are limited to roughly a dozen neutral tones. Most museums still consider rag mats to be the industry standard.

Matting Tips

Standard Matting
It is important that the beveled (inside) edge of the matboard overlap the artwork by at least one-eight to one-quarter of an inch. This is necessary, since humidity and temperature changes will cause paper artwork to expand and contract. If the mat overlap is insufficient, the artwork will cockle and bow through the front of the mat. Keep this in mind when sizing your mat.

Mat Sizing - We prefer wider mats (4" or greater) because they lend importance to nearly any piece of artwork. Customers may be tempted to go with a narrow mat, hoping to save money on the mat and moulding by making the overall piece slightly smaller. This almost always makes the mat package look crowded. Small prints and photos (particularly black and whites) benefit greatly from bigger mats.
When calculating mat sizes for limited edition prints, monotypes or any valuable work on paper, it is important to remember that the outer dimensions (template) of the mat must be large enough to accommodate the paper - do not trim the artwork's border to fit the mat. Even if the image is unaffected, any trimming diminishes the value of the piece.

Mat Design - As mentioned above, one element of mat design is the use of wider mats. Unbalanced mats can also create visual interest. An 8" x 10" sepia or black and white photograph would look good in a white, deep bevel mat 6" all around, but the same photo with weighted bottom mat (7 to 8 inches on the bottom, 6" sides and top) would be more striking. Any number of unbalanced designs can be incorporated, depending on the artwork.

We are also partial to historically correct matting for older artwork. French matting, which consists of neutral mats decorated with any combination of watercolor wash bands, marbled papers and colored lines, is ideal for antique botanicals, natural history prints, architecturals, maps, etc., although it can work with other types of art as well. (Examples of French matting can be seen elsewhere on this site.)
Fabric-wrapped mats are another way of adding texture and color in framing design. Silk, linen, suede, moiré and even burlap and denim can be used to great effect, particularly on deep bevel mats or when used with a wood fillet.

Floating Artwork - Floating a piece of artwork can be an effective way of making the piece stand out. Artwork printed on deckled edge paper really benefits from floating, since it is often the intention of the artist to present his/her work on good quality paper that has a hand-made appearance. When floating deckled edge artwork, we prefer to mat one-half to two inches from the edge of the artwork. It is important that the artwork not touch the glazing material in front of it; any floated artwork should have at least a single mat as a spacer. If no mat is used, spacers must be inserted along the frame's rabbet.

Another floating technique is to have the artwork "float up" from its backboard by mounting it on a support approximately one-quarter of an inch thick. The support is cut slightly smaller than the artwork so that it is invisible, making the art appear to float just above the backboard. A mat can then be cut wider than the artwork (just as it would with a deckled edge print) and floated on a slightly deeper support (three-eighths to half an inch). The overall effect is to create depth within the frame package and showcase the artwork. We feel this is an especially striking way to display Japanese woodblock prints.