Re: "Boric acid" and gum
Well, damn, Ryuji, Back to glut being the best hardener on the market, huh :)? Thanks for turning me onto it. I'll email your post comments, below, to the chemist. Chris To see if borax would do, what you needed to do is to make a boric acid solution, titrate with NaOH to the end point pH of about 9.2 at 25C, and use this as if it were borax solution. (because it is identical to borax solution.) In reality, the active agent in the crosslinking mechanism above is borate, not boric acid, and the pH of 9 or higher would be most effective. (At pH of 9.18 at 25C, 50% is in borate form and 50% is in boric acid form.) Crosslinking of PVA or other polyhydroxy polymers with borate is via condensation reaction, which is quite different from how common gelatin hardeners work. As it is condensation reaction, the crosslinking is easily reversible by changing the pH or adding more water. In photography, hardener is defined as an agent that suppresses swelling of the polymer binder when immersed in water or other processing solution. Even if you can make a thin film layer of gum-borate coating, it will swell (and dissolve away, as you noted) once immersed in water (as I described above) and it won't qualify as a hardener, even though borate crosslinks the polymer. -- Ryuji Suzuki http://silvergrain.org
|