Re: Gum & the commercial ?
At 7:43 AM -0700 11/3/06, Christina Z. Anderson wrote:
Halvor said:Yes--the British Journal of Photography from 1850's on--I'm now up to 1930 this week (it wasn't called the BJP in the beginning). But the chloral hydrate and glacial acetic acid were Herr Watzek's formula in the Weiner Photographische Blatter (whatever that might be). It is gelatine 40 grains, chloral hydrate 25 grains water 100 minims.(possibly chloral hydrate or acetic acid to allow cold dev of gelatin)I had forgotten about pH influence on "solubility" of gelatine, this calls for a few more days in the lab :-) Is there any best article or well referenced starting point for this subject? (overview & history of the praxis of "gum printing") -
I don't know what it is but you can only get it with a prescription. Back in the days when I was printing gum I convinced my dentist it would be good for my teeth and got a bottle of it. If you have any need of it I probably still have it somewhere in my chemistry stash. Used as Watzek recommended it hardens the gelatin slightly making it necessary to develop with some type of force, say by water spray or scrubbing. I never managed to get it right, however.