Museum Grade Prints/Poster Storage Boxes 16-1/2 x 12-1/2 x 3" BLUE-GRAY. Drop front. Use for 12 x 16" prints. The archival material used for these boxes is 60 point, solid-core, acid-free, lignin-free cellulose fibers. It is buffered with a 3% calcium carbonate, which blocks migrant acids, The boxes have a pH of about 8.5. They have metal-edged corners and ship assembled. Boxes have passed the Photo Activity Test certifying that they are safe for the indefinite storage of photos.