Let me dumb this down, more or less pH is a measure of the acidity or alkalinity of a solution. Less than seven is considered acidic and greater than seven is considered alkaline, pH 7 is considered neutral. In biblio terms neutral is good. I won’t bore you with the details they are out there on the net. Every paper conservation lab worth its salt has a decent website devoted to showing their endowers exactly what they are doing with their money.
Feel free to write in and correct me . . . books made before the industrial age, I mean ones made with paper made from cloth fibers and book leathers, are more chemical stable than books made after the mid 19th century. Why? cause once you start cranking out millions upon millions of books to feed to the unwashed masses, you start using wood pulp for paper and buying your leathers from the same folks who upholster buggy seats. You can do the math. Since then, allowing for publisher’s whimsy things haven’t changed all that much.
The reason I bring this up is that when you are thinking of using a product on a book, you should have a good idea of its relative acidity. It may not actually cause damage, but why make things worse?
I bought some litmus strips to do some product testing. Elmer’s Glue comes up about 5, just like on the Materials Safety Data Sheet said it would, and as expected pH neutral Adhesive is just that. Aside from what I have in my desk, I invite folks to suggest other stuff for me to test. Mind you since you are measuring its acidity RELATIVE to neutral, you can only measure stuff that has water in it. So, things like Heptane, naptha, Deacidifying sprays can’t be measured this way.