Andrew-where did you post your comment on the DPUG site. I could not find it.
David-Why does this solarization only happenen on a few prints?
The humidity level is very low here in Ohio right now. Could that cause it? It seems strange to have this happen on just certain prints.
It the issue consistent with a particular negative with each print and at a consistent time of exposure? If it's isn't consistent, then perhaps its the amount of sensitizer on that particular part of the paper? Your negative highlight values may be too dense and take long to print through thereby causing too overexposure in the shadows.
I've often thought that it's also related to using too much sensitizer as well? Not sure, but just a hunch.
However, using gold, platinum or palladium toner will instantly make those areas disappear!
I'm pretty sure that the solarization has nothing to do with low humidity though.
David