A comment made in a separate post warrants further exploration. The question is whether mounting any print to glass or acrylic would be harmful to the print over time. Glass is a highly stable material, which if clean, will not leach any compounds that would be harmful to a print. Glass is made mostly of silica and is impregnated with metal ions. All of the materials in glass are, for the purposes of this discussion, stabilized and nonreactive, and certainly won't compramise the archival nature of any print from a chemical reactive standpoint. I should think this is the same with at least most acrylics, but I'm not quite positive about that. If anyone knows why acrylic would not be an archival mounting surface from a chemical reactive standpoint, please explain in detail. The only way I would think, in theory at least, that glass or acrylic, if used for mounting would be harmful would be either by way of thermal expansion, ie. due to a large coefficient of thermal expansion (COE), or by way of transmittance of UV, light, or other EM radiation. With a high COE, moderate changes in temperature could potentially cause contractions and expansions that over time would place internal stress on the printed paper (or other material) and compramise it's structural integrity. Perhaps something like 100% cotton museum board escapes this fate because it is not rigid as are glass and polymers such as acrylic, and as such does not expand and contract on a macroscopic level with changes in temperature and therefore doesn't place any stress on the printed material. With these things said, if anyone has any evidenced-based thoughts as to why glass or acrylic are not archival mounting materials, please describe...thanks!