"Boric acid" and gum
"I had the joy of being in the bromoil class with a chemist physician who practiced whatever that field of medicine is where they determine risk and safety stuff at large corps. Anyway, he was a wealth of photo lore. One thing he told me was that the slime goop that kids play with is none other than gum arabic (or even PVA in some cases) mixed with boric acid. Boric acid makes gum go instantly hard (gum viagra?). Jim suggested using this as a sizing. Coat the paper with gum and then harden it in a 1-2% boric acid bath. As a person offlist reminded me, though, when I added acids to my gum mix I got more and more staining/non-exposure hardening in my gum layer as per the example on my website in the learning section on gum, so it may be an iffy proposition. I wonder if the residual boric acid would then affect subsequent gum layers, making it unsuitable for gum, but certainly this was a less toxic form of sizing to dink around with.It's called SLIME; it's a viscoelastic gel that boys love to gross girls out with. It's made by mixing PVA with borax (sodium borate) which is alkaline, not with boric acid. It's an experiment that's used to teach an easy lesson about polymerization, and results in a product that kids love, so it's a great science lesson for kids. Generally gum isn't used for this experiment because the results aren't as predictable as with PVA.