[Frameworks] Advice on removing dyes from emulsion, but not emulsion

[Ugo Bo]

Hallo everybody, I need an advice.

It happens that I have some cans of old negative color stock (Eastman Color
Negative Film 7291, Eastman EXR 100T Color Negative Film 7248, and
something not labelled) that I want to use for painting on it.

I usually paint with watercolors ("Talens Ecoline"), emulsion side, on
black and white stock: paint goes inside emulsion and there it stays:
projector doesn't remove it, neither it scratches it, and I really like
results (1st strip on the left).

Now I want to use these negative color stock that I had for free. Getting
rid of remjet was quite easy: baking soda does the job easily. The problem
is getting the film clear transparent, or at least of a neutral pale gray.

The problem is the orange mask: if I only fix the film I get a transparent
orange film, quite nice, but not fit for painting (2nd strip from left)

I tried to bleach with permanganate bleach and clearing with sodium
metabisulphite, exactly like in reversal b/w, but what I got is a jellowish
surface: better than orange, but not what I want. Bleach removes silver,
but not completely orange dyes (3rd strip from left).

I tried also to bleach with householding sodium hypochlorite: I got a
perfectly transparent clear film, but hypochlorite removed also gelatine,
so you can't paint it with watercolor (last strip, on the right).

Anybody has some suggestion how to simply and cheaply get a clear
transparent film from color negative stock, like the last one, but without
removing emulsion?

Many thanks!
and happy new year
Livio
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