Re: My own PVA glue sizing experience (attn: marek + the gum woesagain)
Loris can speak for himself, but I have never seen a dark reaction in a mixed emulsion, and like Keith, I am skeptical. Dichromated colloids in solution behave very differently chemically from dichromated colloids coated into a film. Three or four years ago, when I was studying the chemistry of dichromated colloids in depth, I could have given the details from memory, but now I'd have to look it up, but if there's a "dark reaction" in dichromated gum solution, it's not anything like the dark reaction in coated paper. I've kept a mixed emulsion for as long as eight hours without any problem, printing from the same emulsion for a long day; that's the longest I can say from observation. This is in the same conditions (ambient humidity >85%) where a coated paper would become entirely insoluble from the dark reaction in less than four hours. I mix my emulsion in very shallow dishes; if I leave a mixed emulsion overnight, it just dries up in the dish.
On Oct 28, 2009, at 5:23 AM, Keith Gerling wrote:
"BTW, it's not a good idea to keep the coating solution (gum/pigment +