What can be done about it?

by Laura Stirton Aust

Have you ever seen a dark brown line framing the image of a print?  What about a thick band of discoloration covering the full width of the margin?  This staining is probably Mat Burn.  Mat burn is caused by an acidic window mat.  It is the cut edge of the matboard which is most acidic and damaging to a work of art on paper.  It isn't always visible on matted and framed works.  But, an acidic mat is a slow fire which burns paper, marring its appearance and reducing its value.

The first window mats were probably made at the British Museum in the 1850's.  Window mats were then used for prints which were removed from books for framing.  Before this time the display of prints was not fashionable.  But, as framing prints became popular acidic mat board began to make its mark.  After almost a century of poor quality matboard stock the paper company Andrews, Nelson, Whitehead started manufacturing a cream colored mat board which was all cotton.  This was the first rag board and was made specifically to protect framed works on paper because it was acid-free.  The demand for acid-free mat board increased as knowledge of preservation and conservation grew.  In the late 1970's alpha cellulose boards were developed.  These mat boards are similar to rag board but are made from the far cheaper pulp of trees which is purified to remove lignin and other non-cellulose material.  Acid-free or archival quality framing materials are more expensive and used by many framers only upon request.  Because non-archival matboard is still used today and acid-free matboards have only been in use for less than 50 years, mat burn on works on paper is extremely common. 

Acid breaks down paper fibers, causing irreparable damage.  To stop the chemical reaction of acid in paper, non-archival mats must be removed as a first step.  Whether or not conservation treatment is necessary will depend upon the work of art, the strength of the paper and the stability of the media.  Treating mat burn may include neutralizing acids with water baths or de-acidification.  Trying to restore a damaged artwork through chemical means may diminish what is visible of the mat burn.  However, it often weakens paper fibers.  Therefore, de-acidification and bleaching are considered only after the mat burn damage has been done.  Preventing mat burn by acting proactively is the safest approach to conserving works on paper.

Most prints have a margin of several inches top, bottom and sides.  A window mat hides some of the margin and may hide the mat burn, also.  But, drawings and documents can have little or no margin.  These works often look best "floated" on matboard in the frame without a window mat to hide the edges of the paper.  On these pieces mat burn is particularly disfiguring and may be distracting to the eye.  Bleaching of the stained areas is the only way to visually recover some artworks and documents with mat burn.

If you think there are acidic mats on your works of art on in your collection, have your framer remove the mats and replace them with acid-free materials.  Or ask a conservator to look at your collection and advise you where to begin.  Removing acidic mats may be the first step in putting out a fire in your collection?

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