I've spent another afternoon in the laboratory trying to get a readable print with Poitevin's process. I posted a plea for help on apug but no luck so far. To advance any further than I have with my efforts I'm going to have to suck it up and buy A Treaty on Photography which will hopefully have some more tips. The failed procedures after the break.
All of the tests started off with 'arches cover white' printmaking paper that was preshrunk and sized with a gelatin/glyoxal subbing that was brush applied. I then mixed up a 5% solution of gelatin (7 grams to 150ml of water) and heated it to 140* f until the gelatin was melted. I took 15 ml of the melted gelatin and added a 1/4" watercolor pigment and mixed until blended.
I brush applied the pigmented gelatin while it was still warm on to the paper. The gelatin needs to set up on a flat surface.
Attempt 3: Failure
I brush applied the sensitizer and let dry. The test exposure was for 30 minutes, and developed in hot water.
Attempt 4: Failure
I brush applied the sensitizer and let dry. I exposed with the test wedges for 10 minutes and developed with boiling water. Some wedges can be made out in the print.
Attempt 5: Failure
I brush applied the sensitizer and let dry. I exposed with the test wedges again for 5 minutes. I developed with boiling water and initially had some visible evidence of a print, but that washed away with more boiling water when I tried to clear the rest of the print.
To try and remove as many variables as possible I tried two other experiments. The first was to run boiling water over some of the un-sensitized paper coated with pigmented gelatin. The gelatin dissolved rapidly leaving no stain.
The second test was with a scrap of the sensitized paper that had not been exposed to light. That did not dissolve under boiling water leading me to conclude that my problem lies with the sensitizer.