I used a 3:1 ratio of gum to sensitizer.
The step chart goes from 100 black to 0 white in 20 steps.
I made 6 exposures from 30 seconds to 3 minutes in 30 second increments.
It was developed face down for 15 minutes with one change of water after three minutes. I then gave it a rinse with soft running water. It was put in the sun to dry before painting.
After drying, I applied a complete coverage of lampblack oil paint and then rubbed off with paper towels until it was a clear differentiation between exposed and unexposed gum. Then, after a quick soak to wet the paper, it went in a 15 second bleach. I used Clorox concentrated (8.25%) diluted to 6 percent and then mixed 1:6 with water. Another gentle rinse took it to this point.
The 30 second exposure was not enough to harden any of the gum. 1 minute showed hardening down to about 45 and 1.5 minutes down to 60. The highlights also cleared best at 1 minute.
I think about 4 more steps (of 20) were clear from the 1 minute exposure and 3 from the 1.5 minute exposure. Longer than 2 minutes, maybe only and additional step cleared and not very well.
After drying, I attempted to apply a second coat of oil. To differentiate the two applications, I thought I would choose another color. I chose, Van Dyke Brown. I am not sure why, but it was a disaster. First it was very stick and hard to apply. Then, when rubbing it with paper towels, it pulled off paper, black oil paint and the kitchen sink. It was sticky like glue. When I rinsed it, it came right off without any bleach. Very strange indeed.i won't use that color again.
Anyway, I think that this has shown me that 1 minute to 1.25 minutes exposure works best. If less shadow is desired, the negative could be leveled to lift them to around 85 (from 100).
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