I’m so glad you brought this up. We have seen this phenomenon as well. I’ve noticed it particularly with lithics (chert and volcanic) as well as charcoal. Ours were all archival quality 4mil and 2mil; I’m wondering if the bags aren’t really archival? Perhaps the method of manufacture incorporates some sort of non-archival layer between the layers of plastic that reacts with salts or acidic sediments?
Laura
