[alt-photo] Re: casein image

[Peter Friedrichsen]

Alberto,

I make up my casein emulsion to be about 10% by weight of casein in 
water. I originally alkalized it with household ammonia but later 
switched to using a "pinch" of sodium bicarbonate in a 10% emulsion 
of about 120 ml total vol. I then dilute the 10% casein with an equal 
portion of dichromate as 10% potassium dichromate solution, so the 
final casein is 5%. The pigment load is judged by tint strength when 
brushed onto a white enameled surface as I do not have a milligram 
scale which would be a requirement for the 4 or 5 ml volumes that I 
mix up since I use dry pigments. I occasionally vary the dilution of 
casein and find that the tonal scale expands upon dilution but at the 
expense of image density.

Peter Friedrichsen

At 10:19 AM 04/04/2011, you wrote:
>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
>_______________________________________________
>Alt-photo-process-list | http://altphotolist.org/listinfo