Artlady:
Foam-center board is too rigid? That's the first time I've heard that. What's the problem with rigidity? It seems all mount boards would have some rigidity, but that doesn't necessarily equate to their coefficients of expansion.
Why would the mount board/ backers need to "move" with the art, anyway? If it is properly hinged or otherwise properly mounted, it is free to expand and contract without restriction, no matter how rigid or stable the mount board.
ArtCare was a "major" topic of discussion on another list some weeks ago. There, two conservators responded that independent labs' ArtCare tests (paid for by Bainbridge) seemed valid and that they both recommend the products for most Archival/Conservation/Museum/Preservation(ACMP) framing. Tests are still underway, and results are dribbling out of the labs. Aboput the only thing certain, so far, is that the high zeolite content (clay) does *not* add to the abrasive quality of the boards. Tests have shown conclusively that ArtCare boards are no more abrasive than common alternatives.
Bainbridge says that the zeolites are not only effective filters of migrating contaminants, but that they also, in many cases, cause chemical breakdown of contaminants. That is, the bad chemicals are converted into inert ones. This contributes to their claim that the zeolites' capacity could not (in several lifetimes) "fill up".
Bainbridge was quick to point out that their ArtCare boards, now considered to be the best for ACMP framing, are not a cure-all. Calcium carbonate buffers, UV filtering glazing and other preservative precautions should still be taken, as always.
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James Miller,PPFA-CPF; PPFA Certification Board Member; FACTS/GAFP Committee Member