AboutJennifer Pierce Expertise I can answer any questions related to picture framing, art display, or art installation, including very large pieces, canvas stretching, shadow boxing, needlework mounting, and just about any type of dimensional or non-dimensional artwork display. The only questions I cannot answer pertain to fine artwork restoration (e.g. your Van Gogh oil painting is faded and you want it to be restored to the original brilliance--call a reputable museum for that).
Experience I have been in the picture framing business since 1987, with a specialization in hospitality (hotels) and commercial office installations. I have worked on artwork for nearly every major hotel and design firm in the world and have designed some pretty wild installations. Additionally, I have experience with almost every type of conservation technique
Education/Credentials All of my education was acquired in the field.
Question I have an original lithograph from a renown Swiss artist that I had museum mounted and framed twenty years ago. Recently I disassembled the piece to discover that there was discoloring where the mat met the paper. The piece was never in direct sun light or exposed to any harsh environments. If acid free mat was used, is it possible for discoloring to still happen? I suspect that the mat was not acid free. Does this effect the value of the work?
Answer Acid burn can and will cause discoloration to paper art. You can generally tell whether an older mat is acid-free by looking at the bevel on the window; a cotton rag acid-free mat should have a stark white bevel with no yellowing. A rag mat also feels different from a paper one. (This method isn't as reliable with newer mats because a product called "whitecore mat" has been introduced. This type of mat is not acid-free, it just has a white core which produces the white-white bevel. It's sometimes difficult to tell which is which, even for experienced framers.)
How does the backing look? It sounds like from your description the problem is the mat, because you've only seen discoloration where the mat touched the art, but sometimes the backing is to blame. It could be that the mat was acid=free, but the backing wasn't, and the pressure all the way around sent the acid through the back of the piece. Does it look worse on the back? If so, that's a good indicator that it was probably the backing. Either way, it's good you got the piece out of that framing package when you did.
I wouldn't re-use that mat or backing regardless. If the artist signed the mat, have it put in a pocket on the back when you have it reframed so you can keep it with the piece.
Acid burn will look yellowish or brown (think old newspaper). If your discoloration is not yellowish or brown, it might be something else. If it's black or greenish it could be moisture damage, which can occur even when a piece is conservation framed. It doesn't sound to me that moisture is the issue here, though.
Discoloration can certainly affect the value of a piece. I cannot speak to the value of artwork; my expertise lies in display only. I recommend you take it to an appraiser who specializes in the genre into which your piece falls. It's possible that in this case, the edges of the paper won't matter as much to a collector, as long as the piece is still displayable.
