"Boric acid" and gum

[Katharine Thayer <kthayer@pacifier.com>]

> "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.
>
> But ANYWAY, is it possible to do some sort of boric acid/gum thing  
> with your class and allow them to make goo to play with? What is it  
> called, GAK?"
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.

kt