Thank you for that informative response!
Is there a way to test if materials are lignin-free?
RE: anything getting on the folders to result in an acidic reading.. these are fresh out of the box and unhandled. It is particularly strange to me because the reading stays as “nuetral” for 5-10 minutes, and then gradually fades to “acidic” over time after that. The mark is fully in the acidic range by 20 minutes or so. Quite strange.