Direct carbon on glass process

[AndrewBurns]

FYI here's two exposure tests, one with cyan pigment and the other magenta. For fun I flipped and stacked the two glass plates so that the gradients overlapped and blended together.

The colour plates are pretty vibrant, happy with the results so far. I plan to expose and develop the yellow plate tonight.

 

[AntonKL]

If you replace acetic acid by tartaric acid, you will have the system Poitevin introduced around 1860.
At a ~ 4 : 1 (ferric chloride : tartaric acid) weight ratio the warm gelatin solution will not coagulate and can be used for coating.

They used to use this as a positive process, by toning the unexposed parts with gallic acid. The exposed parts became more soluble which aids clearing, to amplify this they let the gelatin/ferric/TA mix hydrolyze for a couple days before coating. See e.g. ch. 8 in Die Lichtpausverfahren, die Platinotypie und verschiedene Kopierverfahren ohne Silbersalze (not sure if that link works from outside of Germany).

Perhaps fructose would work - it also forms a light sensitive complex with FeCl3 and its thermolysis products are effective crosslinkers (sadly also effective at staining).