U of S | Mailing List Archive | alt-photo-process-l | Re: Gum Preservatives

Re: Gum Preservatives



On Dec 7, 2006, at 4:56 AM, sam wang wrote:

I have no experience in killing my own wild boar nor grinding my own corn, but my experience with the commercially made gum solution has been awful. One batch may be OK, then gallons afterward simply did not dissolve, with or without dichromate and exposure.
I can't parse this sentence, sorry. You're saying that in your experience, gum that comes already dissolved won't dissolve? That makes no sense to me. Even if you mean that once coated as a film and dried, the unexposed gum won't dissolve, that doesn't make sense to me either. If it was dissolved before it was coated, there's nothing I can see to keep it from dissolving again after it's been dried but not hardened. Perhaps you're suggesting that they used a crosslinking agent for preservative and used too much of it, preventing the gum from crosslinking further when exposed, but that makes no sense to me either; if it was crosslinked that much, I doubt it would be soluble in the emulsion. Or perhaps it's something else about the preservative interferes with the crosslinking of the gum once coated? That last is the only reason that I can come up with that would be plausible, but I've never seen it in all the different commercial gums I've used and tested.

I personally don't like the cheap (well, they used to be cheap, but as Judy says they're getting more expensive now) dark lithographers' gums, that are full of particulates of unknown nature which I call gunk, but to my surprise even these print nicely, and the hardened gum (when printed unpigmented) is as clear and clean as gum that started out clear and clean. I do have to admit I've only tried two samples of this type of gum. But it seems to me that gum that won't dissolve wouldn't be useful to printmakers either. And it's odd that if prepared gum won't dissolve, there haven't been more reports of this in the decades that people have been using the stuff for gum printing.

This is not to dispute your observation, certainly, but only to say.... I don't understand it.




Same as why I use 1/5 of dichromate compared to everyone else. But we won't go there.
Interesting, how people will throw something out like that and then say "but we won't go there" to discourage any response. Sorry, you already went there, and when you go there, you don't get to say "we won't go there."

http://www.pacifier.com/~kthayer/html/Dichromate.html
Katharine




Mark is in Toronto teaching a workshop with Sandy. Otherwise I fully expected some wise speculatiions on Smellographs, Odortype...


Yes, Judy, wasn't it just yesterday that we had the exchanges? Have these kids today even heard the term "gungho" before? Gosh.

Sam

On Dec 6, 2006, at 11:41 PM, Judy Seigel wrote:


On Wed, 6 Dec 2006, sam wang wrote:


There are many preservatives that can be used. Judy suggested formaldehyde. Thymol works well enough for me except when I put in too little - I wanted to put in a minimum amount. The smelly gum printed fine, maybe even better than fresh. I hope you didn't throw out your spoiled gum.

Maybe there's something about mixing your own gum arabic like killing your own wild boar or grinding your own corn, but I like to get a gallon of lithographers gum & then another gallon from the same lot if I like it... It works fine (as far as I know) and the poison is already in it.

However, as a beginner I did mix gum (Sam, did you REMEMBER that? Uh oh!) & found that one drop of 40% formaldehyde per 2 ounces of whatever the mix, kept the gum seemingly unchanged for years. But now formaldehyde is difficult to get in the US ... I had a prescription from a friendly MD. (It's used for athlete's foot, or was.)

But that $17/gallon gum from Daniel Smith is now I understand about $50/gallon (either the drought, or the prevalance of gum printing driving up the price), so it could make sense to mix yr own.

I think it was Chris marvelled at early gummists tolerating the odor of sour gum... but EVERYBODY & most places stank to high heaven in the days before laundromats, hot running water & flush toilets.... Mere gum arabic was probably drowned out.

Judy