Acid free is always an issue with watercolor papers.
Maybe printing requires a different composition than single sheets of paper. Never heard of this alkaline substance before.
Needs further exploration for the artist's sector. Interesting.
" Sometimes one comes across paper marketed as "acid-free". This must have been supposed both by some paper sellers and some publishers to be a mark of quality. But absence of acid in a paper does not guarantee any permanence, unless it is backed up by a deposit in the paper of an alkaline substance (usually calcium carbonate) to counter the influence of acids from the environment and acids produced during paper degradation.
Permanent paper and lignin
The reason for excluding lignin as a component of permanent paper is now again debated. The debate is part of an understandable trend, known from many technical fields, urging for a move from composition to performance requirements."...etc.
