Backglasses can be cleaned on the back, but only very carefully in the
clear areas, such as the tiny little windows where the scoring reels or
displays show. Any cleaning in other areas may damage the ink, or white
mask such that you will greatly regret even having considered cleaning
I recommend using Q-tips and rubbing alcohol or glass cleaner sparingly to
the clear areas only. Apply the cleaner to the Q-tip only and then rub
slowly and carefully with the Q-tip. Do not spray the cleaner directly
on the glass. Be careful not to use so much liquid that it drips. You
must not let the Q-tip or cleaner touch the edge of the white mask or any
ink. I prefer using a very bright light up close to ensure that I get it
clean and don't goof. Usually it takes several Q-tips and to do it right.
Use a lot of patience and you will be pleased with the results.