From: Judy Seigel (jseigel@panix.com)
Date: 11/17/02-01:45:44 AM Z
On Sat, 16 Nov 2002, Temi wrote:
> Gum Dichromate - Two Questions
>
> No. 1 - When making gum prints, what are the pros and cons of using
> either Potassium dichromate or Ammonium dichromate.
Temi, If you use them at the same concentration, there's not much clear
difference between the two. There's been a lot written about their
relative strength, staining, sensitivity (or "speed"), but unless the
percent solution is mentioned that's like saying coffee is hotter than
beer...
Potassium dichromate is soluble in water to about 11%, ammonium to about
30%, but my tests show that if you compare both at the SAME percent, say,
10%, differences are minor, or from what you were wearing that day.
I find it convenient to keep ammonium dichromate at 26% and dilute
variously at use... But in some cases it's harder to get, because a great
deal of silly nonsense is perpetrated about its being a fire hazard, so
you may have to pay hazardous shipping charges, and/or more per pound.
For whatever reason, most places the ammonium is about twice the price of
the potassium (maybe more). But a pound can last for many years, so it's
not a big item.
I've said this a bunch of times on the list, by the way -- seems to come
up every 6 months or so.
Judy
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