[alt-photo] Re: casein

[Alberto Novo]

> Continuing my casein exploration. Today I went to use my nickel azo yellow stock solution and here is what it looked like: 
> 
> http://christinaanderson.visualserver.com/Text_page.cfm?pID=2076 
> 
> not a problem with thalo and magenta (yet). 
> 
> Interesting.
> Chris

"It combines readily with bases forming compounds, and resembles albumen by
being precipitated by the metallic salts, and forming with them two
combinations, namely, one of casein and the acid, and another of casein and
the metallic oxide."
(quoted from Richard's post) 

This is the answer to your question: the interaction between nichel and 
casein. The same should happen with copper, manganese, chromium and other 
metallic pigments, like verdigris, manganese violet, raw and burnt umber, 
viridian green, hematite, Mars black and other iron-based earths, etc.
But I think that they require some time to react with casein, like in your 
experience. 

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