PVA for gum printing (Re: Artistico Unsized?)
For whatever it's worth, PVA (polyvinyl alcohol) has long been used as a substitute for gum; since dichromated PVA apparently behaves chemically like dichromated gum arabic (the crosslinking mechanism is assumed to be the same) the research on dichromated PVA is what we use to try to understand the chemistry of dichromated gum, since there's virtually no research on the mechanisms of dichromated gum per se.
There are many variations of PVA and not a consensus on what PVA works best as a substitute for gum in a dichromated colloid process; it comes in an endless variety of types depending on molecular weight (length of chain) and degree of hydrolysis among other characteristics.
David Hatton, several years ago, provided us a wonderful link to a site that explained how the different PVAs behave, depending on their different characteristics. I went looking in the archives for the link and actually found it (my success at finding things in the archives hasn't always been so good) but when I clicked on the link, it took me to a page that was all in perhaps Korean, so I guess that link doesn't work any more.
Mike Ware, several years ago, shared with me some research a student of his did to determine what PVA works best for gum printing; he gave me permission to share that information, with proper citation. Here's an excerpt of the post where I shared that with the list, gleaned from the list archives:
"He said that they settled on was a "polyvinyl alcohol-acetate; i.e.
only partially hydrolysed co-polymer, which is much more easily
dissolved in water than the pure alcohol. We found an 88% hydrolysed
PVA, with an RMM around 25 kD in 20% w/v solution, to offer the best
all-around results-- comparable to a 14 Baume Gum."
"If you make any public use of this information in the future, please
acknowledge the original experimenter, by citing:
Stephen Beckett, M. Phil. Thesis, University of Derby (UK), November
1993. (A private communication from Mike Ware)."
Just out of curiosity I tried printing with PVA some time ago, in the form of "gloy." Keith Gerling was kind enough to share a thimbleful of his supply of gloy with me, so I was only able to make a couple of small test prints, but in that limited experience, I couldn't tell any great difference from gum. It looked like gum, felt like gum, coated like gum, printed like gum (same exposure as my usual, same number of steps (8) compared side by side with my gum of choice at the time, using the same pigment mix, etc.
On Aug 25, 2007, at 6:37 AM, Dave Soemarko wrote:
First time I heard of it. I just did some search, and it looks interesting.