For over thirty years as a bench jeweler, there are two items I
wouldn't be without. First is powdered Lye, available at any grocery
store. This in hot water in the ultrasonic will easily remove the
gunk that customers come in with, plastered on the back of their
diamonds. I used to use Drano but it contains small bits of aluminum
that sometimes turns gold black.
The second item and the one that will probably remove your glue is
oven cleaner. I put my nasty ring in a beaker and spray it on. Let it
set for about half an hour. Then I rinse it off and into the Lye and
hot water in the ultrasonic for final cleaning. This is also a great
way to clean diamond rings prior to retipping.
Hope this helps.