Laura Stirton Aust, Paper Conservator, ARTcare

Whenever possible, prints should be matted for protection both in and out of a frame.  Most museums store unframed prints fitted between a window mat and backing. Out of a frame the mat protects the edges of the paper and reduces handling of the print. In a frame, the window mat separates the glazing from the art.  This space prevents the surface of the print from coming into contact with the glazing which could encourage mold growth, media loss, or abrasion.

A window mat has beveled edges which cover the margins of a print when it is over matted.  The opening is smaller than the outside dimensions of the paper, and it reveals the entire printed area.  If there are distortions in the print, over matting will help prevent the support from touching the glazing.  When a print is "float matted" the window mat does not touch the support at all but still separates the paper from the glazing.  Works which are printed to the edges of the paper and those which have been cut down to the plate mark are often floated to reveal the whole sheet of paper.

Window mats may be decorative or plain.  Some are very wide while others are barely visible. Museums usually choose neutral mat colors, and collectors may coordinate mat colors with decor.  The fundamental requirement for acceptable matting is acid-free materials. Mat board must either be rag or buffered sulfite. Avoid inexpensive non-archival mat boards.

UNREFINED wood pulp mat board or non-archival mat board contains acidic materials that will burn or stain anything it contacts.  It is available in the widest range of colors and textures and is the standard sample on many frame shop counters.  But, don't use it. (For more details about this staining, see the Fall 2004 Dieu Donne Newsletter article titled "What is Mat Burn?")

RAG mat board, sometimes called Rag Board or Museum Board, is made from 100% cotton fibers.  It may become acidic in prolonged poor storage conditions and should be replaced if discoloration or foxing is detected.

BUFFERED RAG mat board, also called Museum Board, is made from 100% cotton fibers with calcium carbonate added to neutralize acid from surrounding materials.  This mat board comes in a range of neutral white tones to cream colors.

CONSERVATION mat board, also called Archival, Buffered Sulfite, Alpha-cellulose, or Acid-free mat board, is made of chemically refined wood pulp which is buffered with calcium carbonate.  It is made in a variety of colors.

Only the very best framers will automatically choose rag or conservation mat board.  Rag board is more expensive than conservation board, which is often twice the price of unrefined wood pulp mat board.  If a framer does not offer rag or acid-free mat board, find another framer.  Also, don't let a framer sell you standard unrefined wood pulp mat board which is "lined" with rag.  The lining might prevent contact between the wood pulp and print, but acidic vapors will still out-gas from the mat board.  Since the window mat and backing form a protective package, there should be no acidic materials in the container.

The window mat package should consist of a window mat which is attached to a back mat.  The backing is the same size as the outside dimension of the window mat.  These two are attached with acid-free gummed cambric tape (sometimes called linen tape) along the upper or left edge, whichever is longer.  If the mat is going into storage instead of a frame, a sheet of glassine should cover the art.

Window mats with backings can be purchased pre-cut in standard sizes.  For instance, a 16" X 20" outside dimension mat may have a window opening of 12" X 16". These mats work well for photographs which are usually standard sizes.  -Fine art prints vary in size, which often requires custom cutting of window mats and backings.

For those who are willing to invest many hours in practice, mat cutting skills may be developed.  But, routine practice is necessary to remain competent.  For more information and detailed instruction on mat cutting consult Anne Clapp's book Curatorial Care of Works of Art on Paper.  Simple tools, which require the most ability may be acquired relatively inexpensively.  Alternatively, professional tools and gadgets can turn mat cutting into a hobby. 

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