Some years ago when I learned some rudimentary platinum printing, the
friend who taught me used a system she had learned from Alan Newman, now I
believe of Chicago, of NOT mixing up developers for the different
contrasts, but of rather keeping a weak (10%? don't remember) solution of
potassium chlorate in a dropper bottle and adding from one to however many
drops to the mixed emulsion as needed.
This worked very well. Of course we didn't know then that potassium
chlorate was NG, along with so much else we didn't know in the dark ages
of platinum printing a whole 10 years or so ago. But I wonder if it
wouldn't be possible to do something similar with the dichromate? Add
drops to the emulsion as needed.
I find, BTW, that a fairly concentrated dichromate keeps a year with only
gradual loss of speed (in gum printing). Also, for emulsion batches that
would have required less than a drop, I added x number of drops of
distilled water to one drop of the chlorate in a shot glass, then used one
drop of that mix.
Judy
>
> Keith has just described one consequence:
>
> >KOx does not become
> >exhausted. I don't know about the dichromate. I have found some green
> >needle-like crystals in one of the bottles.
>
> This is, very probably, potassium tris-oxalatochromate(III): K3Cr(C2O4)3.3H2O
>
> The other consequence is that when the Cr(VI) of dichromate is thus reduced
> to Cr(III) it will cease to have a 'contrast enhancing' effect.
>
> Mike