In lieu of starting a new thread, I hope no one minds if I just append my own recent carbon issues to this thread.
For my tissues, I used the emulsion side of some old RC paper (not fixed out, but long since fogged) and sensitized & exposed them within a week. My result; complete insolubility of the gelatin! It wouldn't transfer, and then after I got frustrated it wouldn't even wash off in hot water.
The smoking gun might be that this glop was kind of old (refrigerated) and has probably been heated up and re-refridged 3 times or so. I've heard that you shouldn't reheat glop too much, so could this be the cause?
Another thought was that by coating it on the emulsion side of RC paper, some hardeners inherent in the paper might've migrated to the goo?