Archival Methods Un-Buffered Archival Tissue, 1000' x 24" Wide Roll Buffered with calcium carbonate 2-3% alkaline reserve, pH 9 0.5,.Acid-free. Un-Buffered, pH 6.5 - 7.2 No calcium carbonate -Acid-free. Light weight 20-34g/per square meter 1.5 mil thicknesses Caliper 0.0012 Passes the PAT (Photographic Activity Test) ISO 14523 (formerly ANSI IT9.16). and TAPPI T444 silver tarnish test Sulphur Content (Maximum) 0.0004