Re: Contrast in gum bichromate

Carson Graves x4692 3NE (carson@zama.hq.ileaf.com)
Tue, 13 Jun 95 13:16:45 EDT

From: Judy Seigel <jseigel@panix.com>

>
> And here is where the issue of bichromate dilution comes in. Although I
> try to be a good citizen and use weaker bichromate, the stronger solution
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
If you convert the hexavalent chromium to trivalent chromium and then
percipitate it out before disposing, there really shouldn't be any
difference. I believe the FAQ has this information.

> is an important contrast control -- the stronger the sensitizer, the
> greater the overall sensitivity, hence the more you hold those highlights.
> However, inspired (goaded?) by Sam Wang's comments, I've been experimenting
> with a brief flash. 5 units on a total exposure of 140 units was too much. (To
> be continued.)

I'd be very interested in hearing the results of your tests, but I
don't think you'll notice any difference other than a baseline fog.
Flashing works for a light sensitive emulsion like silver where there
is a threshold of response to exposure and a significant toe area.
Dichromate emulsions have essentially no threshold and a straightline
response to exposure. But then, I've never thought to test it
empirically, so...

Carson Graves
carson@ileaf.com