[alt-photo] Re: casein image

[Alberto Novo]

Peter, 

> First off, I duplicated Alberto's results of the percentage of casein by 
> weight. I had read that it is 28% by weight of skim milk, (specifically 
> cows milk ) but when I dried it down after separation I noted 23% of dried 
> weight of skim powder which is the same value noted by Alberto. 

Perhaps we were using the same skim milk... :-)
Which recipe were you using for your casein dichromate? 

> What I enjoy about casein is its ability to hold such a high pigment load 
> without staining, when using such a low percentage of actual casein in the 
> emulsion vs gums 30-40%.

I have used up to 0.4 g of natural earth in 10 cc of casein solution + 10 cc 
of ammonium dichromate. 

> ...The best for me is to work with 
> it on the slightly acidic side where its viscosity is less than when made 
> alkaline but not too acidic of course, because the emulsion starts to 
> break down going below about pH 5.5, based on my tests.

Casein is insoluble in acidic solutions. This is why it is widely used to 
etch color TV screens. US patent 4,865,953 "Method for making a stencil with 
a borax-free, low-dichromate, casein photoresist composition" makes a 
solution of casein with:
680 cc 25% sodium hydroxide,
60,000 cc of water and
6,000 g of casein, to wich ammonium dichromate is added from 5 to 15% the 
casein content. To make the things more simple, one could use a 1% sodium 
hydroxide and then using:
17 cc of 1% sodium hydroxide
43.7 cc od water,
6 g of casein. The resulting solution is the same (about 10%), etc.
The final pH should be in the range 6.0 to 7.0. 

Alberto
www.grupponamias.com
www.alternativephotography.com/wp/photographers/rodolfo-namias-group