> That dichromate is bright orange -- meaning, as I say, unexposed.
> > Why doesn't the pigment come off with it? It's held by the
> > darkened, exposed gum in the *lower* layers.
>
Bcause
The gum is porous.
The dichromate dissolves in water
The solid pigment is trapped in the interstices of the porous gum..
That is why the dichromate runs out of the print when you put it in water.
Silver gelatine printing works in much the same way. The exposed and reduced
silver remains in the porous gelatine while the unexposed silver salts are
dissolved in the fixer.
These are such basic aspects of photography that it is quite amazing that
anyone is questioning it.
Terry
Received on Tue Apr 11 04:03:42 2006
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