Natural mulberry tissue. This wood-free and acid-free paper is used by the British Museum and the Smithsonian Institute. Its strong long fibres have the effect of disappearing when glued down to a substrate paper. In recent years, this quality has been used to advantage by printmakers and painters for works on paper. 25gsm: This is a very fine light weight acid free tissue paper.Natural mulberry tissue. For use in paper conservation and for printmaking. 30gsm: The fibre is from the paper mulberry, ton saa. Also known by the Japanese name kozo. This is an acid free tissue for use in paper conservation and for printmaking.