Archival Methods Museum Board is made of 100% cotton fiber. Polar White Museum Board has a cool tone with a blue shift, is acid- and lignin-free and incorporates alkaline or neutral sizing. All boards are buffered with calcium carbonate. This ensures protection from the destructive effects of acid migration from the matted work and from a polluted environment that might cause the pH of the mat board to decrease (become more acidic) with age. No optical brightening agents are used in the manufacture of their 100% cotton Museum Board. 4-Ply / 60 Pt. (Approximately 1/16") 100% Cotton fiber pulp (99% Alpha Cellulose). It does not contain any post consumer waste recycled pulp. Paper is free of metal particles, waxes, plasticizers and residual bleach peroxide. Sulfur content is less than 0.0008% reducible sulfur. Iron content does not exceed 150ppm and copper does not exceed 6ppm. No optical brightening agents are used in the pulp Alkaline sizing is used for both internal and external sizing. No alum is used in the manufacturing process Buffered with calcium carbonate 2-3% alkaline reserve, pH 9 +/-0.5, acid-free Color dyes are light-fast and non-bleeding Board will not degrade and cause harm to mounted matted artwork Board passes the PAT (Photographic Activity Test) ISO IT 18916 (formerly ISO 14523 ANSI IT9.16) Lignin content is tested by TAPPI 236 cm-85 and has a Kappa number of less than five The single ply sheet