Test the envelopes with one of the Ph-testing pens (available, for instance, at http://www.gaylord.com/adblock.asp?abid=1655). If they were buffered or lignin-free in the first place, they should stay acid-free, but if they were just acid-free but contained lignin, they will become acidic. We have a lot of boxes with ACID-FREE stamped prominently on them, but they aren’t.
