If you followed my advice on the page Jewelry Turns Skin Black
and you are still having problems, including dermatitis, try this:
clean your jewelry, especially rings and let them dry completely, then
coat the inside or underneath with clear nail polish. This will provide
a barrier between the jewelry and your skin and should solve your
problem.
A Jeweler's Best Friend
The next time you can't get your rings off remember this little tip - spray some Windex on your finger. With a little effort your rings should just slip right off. Windex - a jeweler's best friend.
Side note: if you have been doing a lot of tugging, your fingers will have a tendency to swell. You should let them rest for a couple of hours before you try the Windex.