worked for me!
Some dummy (that would be me) stuck her left hand in a bucket of wet grout while wearing a diamond ring guard.  Grout stuck to the back of the 1/4 carat diamonds, of course.  I tried all kinds of things, but I finally gave up and ordered this stuff.  Soaked for 5-10 minutes, picked up with tweezers out of the solution and rinsed.  After two repetitions and a little scrubbing, took 99% of the grout off.  At least I didn't have to go have the stones removed.  The label does have a bunch of different warnings about how bad this stuff is for you, so be careful with it.
Rating: 5 stars