I need some help from carbon printers here. I have been experimenting with carbon on glass. My pigment was lamp black. I used back exposure of the glass plates in the sun and it all worked very nicely. It really seems so easy. I then decided i wanted a transparent black and made gelatine mix with perylene maroon and phtalo green ( this has been my favorite black for gum printing). It really gave a nice black gelatine solution. I coated a few glass plates, sensitized, exposed, but they were all insoluble, no image was formed. Something was not right, so I remelted the gelatine and covered some more pieces of glass, cut the dichromate and exposure, but with the same end result. The gelatine was insoluble and no image. AT this point I was at a total loss, so I tried a different batch of dichromate, but with same result. Finally I placed a dried, but unsensitized glass plate in hot water. To my surprize the dried gelatine mix would not redissolve in hot, hotter and very hot water. SOmehow one of the pigments or something else in the watercolour paint that I used as a pigment source made the gelatine totally insoluble once dried. I had an extra glop in the fridge and remelted it again and it melted fine.
Has anybody seen that before? Are there some pigments that are not compatible for making carbon tissue? What do people used for transparent black?
As a side comment I find that carbon on glass with back exposure (did I mention earlier that it is all back exposure) is relatively easy, much easier then gum. Gum does not stick to glass, so the glass needs to be treated, gelatine sticks to clean glass very nicely. It is also easier to coat with gelatine as it sets quickly and the plates can be moved from the flat surface.
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