[alt-photo] Re: casein history

[Peter Friedrichsen]

Chris,

I believe that some of the ammonia reacts with the dichromate to form 
ammonium chromate, so not all of the excess will evaporate. At least 
that is how I understand it.

AFAIK dichromate is only stable in an acidic environment so adding 
sodium carbonate would probably create a mix of sodium chromate and 
ammonium chromate and possibly some of the starters if the 
proportions aren't stoichiometric. On addition, if the color shifts 
to bright lemon yellow vs the orange of dichromates, then you are now 
working with chromates.

Peter Friedrichsen

At 10:18 AM 14/07/2012, you wrote:
>Peter,
>Do you think there is a difference when using sodium carbonate vs. 
>ammonia, since ammonia evaporates when coated?
>Chris
>
>Christina Z. Anderson
>christinaZanderson.com
>
>On Jul 13, 2012, at 9:25 PM, Peter Friedrichsen wrote:
>
> > Marek,
> >
> > From what I understand, the dichromates shift to chromates as 
> they are made more alkaline (from your ammonia) and these salts are 
> less reactive especially in the higher pH. That may explain the 
> lessened dark reaction.
> >
> > Peter Friedrichsen
> >
> >
> > At 12:58 PM 13/07/2012, you wrote:
> >
> >> Chris,I have not tried this approach yet, my bag of sawdust went 
> missing. On the other hand I have been making some prints, mostly 
> monochrome for about a year now. I have also made some prints from 
> the one year old casein solutiojn, actually it was more then a year 
> old. Works just fine. It is interesting that the first solution 
> that I ever made turned to be the best recipe.Another interesting 
> tidbit is that I have exposed and developed one day old paper 
> checking for the signs of dark reaction and found none. There is 
> one more piece from that batch that I will let sit for perhaps 
> another day or two before exposing and developing. As to your other 
> questions I read the PF article years back, but did not think of it 
> much at the time (in terms of my own interest). I only got 
> interested in it last year with the posts on the list.
> >>
> >> >
> >> > Also, Marek, you were talking about Fresson maybe containing 
> casein. The amount of casein/gelatin I have come across is 10-30% 
> casein to gelatin. Have you tried it yet?
> >> >
> >> > Chris
> >> >
> >> > Christina Z. Anderson
> >> > christinaZanderson.com
> >> >
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