It probably works similarly to chromium intensifier. Do a search on that. Not sure how well it would hold up after a lot of years, but worth a shot on a reject, thin, negative (if you want to see if it works). If I recall correctly, you'll need to bleach it first, and redevelop in a paper developer (Dektol works). More difficult on negatives that used a hardening fixer. Others with more recent experience (or better memories) may be of more help.