[alt-photo] Re: Gum washing?

[Johnny Brian]

Thanks for the reply. I use 10% potassium dichromate and the prints have a yellow tint, especially in the highlights. The metabisulfite removes the yellow coloration - I would doubt that it is removing the chromium but probably reducing Cr+6 to Cr+3. I agree that treatment with dichromate does affect the "black" level on the image. 

I also found your book very helpful - 
Thanks again,
Johnny Brian

A few gum images -
http://www.flickr.com/photos/52637134@N03/sets/72157628920297751/

I need to come up with a better way to photograph the prints. I think the heavy glass I used to flatten the print for the photograph and the fluorescent lights added a color cast to the images.

On Jan 18, 2012, at 7:00 AM, Christina Anderson wrote:

> Johnny,
> I wash 20 minutes when I clear stain. But since I began to use the lesser strength ammonium dichromate (10-15%, not saturated) I don't have problems with dichromate stain anymore and have not cleared any prints in years. I only clear now when doing side by side testing of stuff or when calibrating gum with PDN because the dichromate stain can look deceptively like increasing maximum black/exposure in the PDN system when, in fact, the gum layer is hardened enough. Hence it will result in your thinking you need longer print times when, in fact, you don't. So clearing is a good idea when determining standard printing time to get your maximum "black" (or magenta, yellow, thalo...)...and, in fact, in all the PDN steps. That brown tone that gets successfully darker can be deceptive.
> 
> Once I tested how "maximum black" dichromate actually gets by leaving a dichromated gum solution outside in a cup in full sun for a day. It gets the color of dark molasses. Silly factoid you need to know :)
> 
> Hmmm...I should have mixed it with metabisulfite to see if the brown turned green...oh no, shades of reading years and years of "what is dichromate stain" arguments in the alt list archives must be getting to me.
> Chris
> 
> Christina Z. Anderson
> christinaZanderson.com
> 
> On Jan 17, 2012, at 5:10 PM, Johnny Brian wrote:
>> Thanks. I have been using 1% metabisulfite as I do have some yellow discoloration. I'm reluctant to change much in the process as I created a calibration curve with PDN - and it seems to be working OK. What I was curious about was to how long should I wash the print after metabisulfite treatment. 
>> Thanks, 
>> Johnny Brian
>> 
> 
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