The thing I dislike the most about carbon printing is sensitization. Issues of waste dichromate disposal, waiting for the tissues to dry after sensitization...I find it tedious, especially for a "hobby" printer. In a more production-oriented environment, sensitizing, exposure, mating, development can all be batched or pipelined to some extent, but I'm not there. And I don't have the possibility of storing sensitized tissues in my freezer.

So I'm intrigued by the possibility of a diazo-sensitized tissue that is stable on the order of weeks (or even more, perhaps), so that I can just make one print (relatively) quickly, when I have a chance. In poking around some dark corners of the internet, I came across an anecdotal report of someone using a screenprinting diazo sensitizer with gelatin. (This was to make dye-transfer matrices, but the principle is the same).

http://tech.groups.yahoo.com/group/d...er/message/123

Not being able to track down the specific emulsion the poster wrote about (Nazdar 101), I used one that was available at my local art store, the Speedball emulsion sensitizer, reasoning, as the OP did, that most of the screenprinting emulsions are probably similar.

Well, I did this, and mixed up a small batch of glop, to which I added the sensitizer. I noticed that the consistency of the glop was different as I was pouring it. A bit thicker, and a little "gummy". Dried for about 44 hours in black or red-safelight conditions.

The poured tissues were completely insoluble. So something went wrong...now I just have to figure out what.

I have a couple of thoughts, and I'd be curious what the collected wisdom thought...

1) The diazo sensitizer used is completely incompatible with gelatin. Not much I can do there except try and find a different option.

2) The sensitizer I used is not stable enough, and broke down over the 2-day drying period of the tissues, hardening the gelatin.

3) I added way too much sensitizer. Despite using roughly the same proportions as the message I referenced above, the chemicals were sufficiently different so as to make the amount I added a gross excess, which contributed to the hardening.

4) Despite the MSDS identifying only the diazo dye and some phosphoric acid (which I assumed would not affect the gelatin in the quantities used), perhaps there was some other substance in the dye solution that caused the hardening.

5) The high temperature of the glop solution (115 F) caused the sensitizer to break down and harden the gelatin.

I'd love to explore the possibilities of this more, but I don't know where to go from here. Any help regarding sensitizer sources (or particular commercially-available compounds to look for), methods, etc. would be greatly appreciated.

--Greg