U of S | Mailing List Archive | alt-photo-process-l | Re: was Miracle size for gum now tonal range

Re: was Miracle size for gum now tonal range

Someone said in the literature recently that gum prints 2 stops (log .6). I was surprised at how low this was, as I always hedge my bets and say 4-6 stops, with 6 a stretch. Partly if you don't clear with pot metabi you can get a false read of maximum black because the brown stain of the dichromate can read a darker step when it is not really hardened anymore "goo" on top. So I always figured that the 2 stop person cleared and found that to be true. Or maybe was guessing it from the seat of his/her pants.

But it's all kind of a moot point I suppose once you fit your negative curve to the exposure/dichromate you use.

I use a 15% solution of am di (2 tsp to 100ml quick n' easy approximate).

So Marek is figuring a 3 stop range, you a 4-5 stop range....

You say that with weaker di and greater exposure you are getting a longer tonal range--do you have a picture on the web of that comparison somewhere?


Christina Z. Anderson
----- Original Message ----- From: "Loris Medici" <mail@loris.medici.name>
To: <alt-photo-process-l@usask.ca>
Sent: Saturday, October 10, 2009 11:47 AM
Subject: Re: Miracle size for gum

Well that is changing the subject but I wanted to note that what works
best for me is using negatives with a DR of log 1.4, 1.5. I presume
you're using a much stronger dichromate sensitizer than what I do.
Weaker dichromate, stronger DR and longer exposure will probably work
just as well as your setup with the added bonuses: a) Better shadows
differantiation (to me at least) b) Ability to use the same negative
for both gum and cyanotype (moot point for tricolors but very handy
for duotone / tritone work which I mostly do)

Anyway, just wanted to mention. Not that this is something carved on
stone -> but it should be noted that there are other options and


2009/10/10 Marek Matusz <marekmatusz@hotmail.com>:
...This one minute thalo test strip
illustrates it very well. You get a full dark and clear whites with about 6
steps on the wedge, negative density of about 0.9. This would illustrate
"gum works best with thin negatives" statement that has been around for so