Direct carbon on glass process

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.

Hologram said:

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.

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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).

AndrewBurns said:

For fun I flipped and stacked the two glass plates so that the gradients overlapped and blended together.

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Very pretty!
The offset phenomenon you were aiming for also comes out nicely.

koraks said:

Very pretty!

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+1

It is a piece of art by itself.

Thanks!

The yellow plate was a bit of a mess, still worked but there was a lot of pigment staining, even with very tenacious development. On a positive note the gelatin is really well adhered to the glass because I was spraying and pouring hot water onto the print from a reasonable height and none of it budged.

I think the staining and overall kinda crappy print is a result of the heroic pigment load Calvin recommends for his yellow colour paste carbon glop, about 60% of the dry gelatin weight! Vs. 16% for magenta and 5% for cyan. I think I might try again with a much lower pigment load, the yellow pigment is already quite opaque so I don't think I need that much pigment to get a strong colour out of it.

The magenta also stained a bit and it also has a fairly high pigment load. I was happy with how that plate turned out, but it was also quite a solid colour in the high-density areas so I feel like it could benefit from a lower loading too.

AntonKL said:

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).

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Thanks very much for the link. It has been a while I have been reading Eder. It is definitely worth a second look!


Fructose looks like something try - pectin might be another candidate.

A few more pics of the colour plates overlapping. I'm going to try again with lower pigment loads on magenta and yellow, but happy with cyan at this point.






On the fence about backlight vs. place them on a very reflective white backing. Putting them on a white backing works quite well for one or two plates but once you get to 3 or 4 the slight colour of the cheap float glass adds up and the highlights look a little grey. Backlighting works quite well for 4 plates as collectively they have enough density for a reasonable black but it would be a bit more work to figure out how to integrate the backlight and present it in a nice way (don't want to have cables all over the wall etc.).

Here are a couple of PVOH- SbQ ( zerochrome) images on glass - back exposed. The biggest challenge is getting an even coat. Phthalo pigment developed well but my carbon black thickened up the PVOH and clotted, and it had to be brush developed. These were laid on a white sheet of paper for light transmission through the back, and photographed.

Also note the contrast difference. The C-blk has more.

Another SbQ emulsion test on glass. Not bad resolution even with the negative sitting 1.5 mm above the emulsion surface (again, back projected through the glass thickness of such). UV Led is a projection config 80 cm above. It is a 25 mm square COB with collimating lens, running at 225 W. Line pairs resolving to 350 lpi., which is pretty good. Exposure 17s. There is bleed. It may be light travelling horizontally through the emulsion as SbQ is not much of a light blocker. I will try with cblk to see if that changes.

PGum said:

Another SbQ emulsion test on glass. Not bad resolution even with the negative sitting 1.5 mm above the emulsion surface (again, back projected through the glass thickness of such). UV Led is a projection config 80 cm above. It is a 25 mm square COB with collimating lens, running at 225 W. Line pairs resolving to 350 lpi., which is pretty good. Exposure 17s. There is bleed. It may be light travelling horizontally through the emulsion as SbQ is not much of a light blocker. I will try with cblk to see if that changes.

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Nice results, what's the dilution of the SbQ you're using? And are you brushing it onto the glass or pouring?

I've tried 1+2 dilution and pouring the layers on but my results were quite variable, I got some good results but on larger pieces of glass there were significant variations in density across the sheet. I suspect it's because as the layer dries unevenly it 'pulls' pigment from other areas.

My PVA- SbQ is made up. I have two viscosities. For these tests, I used my high viscosity grade undiluted. Its probably a little under that of undiluted gum arabic solution, maybe 100 cP ish after adding a pigment dispersion. The best coating I can get with a brush approach is using a thin cut foam rectangle of magic eraser which is ultrafine melamine foam. I just dip the bottom edge and brush with it. It‘s efficient, does not leave a bead at its edge and works well but not perfect. I don’t have a wirewound rod to try but that might be the best way to lay it.

Because it is so viscous, I can get a dense coat easily, but still, levelling could be better. Such a high viscosity does hinder levelling. I can’t say for sure if my viscosity is ideal, but my first goal was laying a sufficient thickness, which a higher viscosity provides.