This response from some previous writing. Those interested should reference my interview with the inventor of the ArtCare board, and see the test results that accompany it. After the tests were made, it was obvious it was a no-brainer to dry mount for archival purposes. The article: http://www.lodimaarchivalmaterials.com/lam/index.html
My understanding is that the molecular sieves in ArtCare board trap the pollutants indefinitely and that under no circumstances are they released. I could be wrong--that is just my understanding and I am not a scientist. But ArtCare materials are still the best way of protecting work.
The tests convinced me that dry mounting provided the most protection to the work. But aside from that, a dry mounted print lies flat and provides a more satisfactory viewing experience for the viewer. And isn't that the point--that when you look at a work of art it looks good and is presented in a away that enhances how it looks--without strange reflections from a print that is not flat.
Azo paper is single weight and dry mounting protects against physical damage. It even protects against physical damage with double weight papers.
And there are other issues. Let's say you print on a larger piece of paper than the image size--an 8x10 print on an 11x14 paper. Now you hinge it to the mount board and overmat it. Surely you would not want to "float" the print. If you did, the border around the print to show--if it were white it would be the brightest thing and would distract the eye, and if it were black it would also be distracting. So you cut the overmat to exactly match the borders of the print. Exactly matching the borders is almost impossible. I don't know about anyone else, but as a photographer I feel I am responsible for every square millimeter of the picture space, the way a composer is responsible for every note. Everything in my photographs count--right up to the edge. If the overmat for a hinged print overlapped the print by even 1/16 (or less) of an inch the delicate balance of tones and spaces would be destroyed. (Maybe not on every edge on every print, but on most of them.) And so I dry mount my prints and float them with an overmat the leaves a border. The matte surface of the mount board is not distracting as the reflective surface of a print with a gloss surface (even a dull gloss surface) would be.
Although I am concerned with archival processing and take every care, the concern with this can go too far. Many paintings from the 1950s are in need of serious restoration. And then, I recall that in 1989 when I was commissioned to photograph a community in South Florida by Art in Public Places, they were restoring a million-dollar sculpture at the airport (also an Art in Public Places project) that had deteriorated because of the pollutants in the atmosphere. The sculpture had been installed only one year before.
Michael A. Smith