I just re-read Adams' Negative, section on intensification, and there is absolutely no mention of hardener affecting the intensification. Though I know with prints it sometimes seems to take a little longer, and sometimes the toning doesn't seem to be as strong as normal, but I have only used hardening fixer in prints a couple of times. So I would go with Adams if no one else posts in the next little while.(posted 8930 days ago)