BOARDS FOR FRAMING
In picture framing, the term "board" generally refers to various types of paper board sheets. Boards are used formatting, backing, mounting, and filler. They are made especially for picture framing.
There are acids in many papers and boards, especially those made from wood pulp. Acids can cause paper and boards to turn yellow and deteriorate (think of an old newspaper), and can cause the same sort of damage to the artwork they come in contact with. Many paper products are "buffered" with calcium carbonate or other chemicals during production to neutralize these acids. Such products are then labeled "acid-free." Buffering is very effective, but may not last forever.
Boards are like art papers, they are made from chemically processed wood pulp or cotton. Cotton is naturally white and acid-free, and therefore requires far less bleaching and processing during manufacturing. The finest papers and boards for art and framing are made from cotton. Matboards or mount boards that are made from cotton are often called "rag," from an old papermaker's term referring to the strips of cotton scrap used in the paper making process.
Matting is a border that surrounds and supports artwork. Matboard is designed especially for picture framing. Most matboards consist of a surface sheet that carries the color and texture of the board, a backing sheet, and several tightly compressed layers that make up the core. Matboard is available in many colors and a number of textures, including simulated linen, marble, and flannel. Matboards are typically 32" x 40", but some are available 40" x 60", and smaller pieces are sometimes sold for the do-it-yourself framer. Matboards are available from art supply and craft stores.