EricP wrote:

And a harmless chemical that attacks part of the glass and gives a
fine etch to it. Sadly I don't remember it's name. Sorry

Dunno about harmless, but ammonium bifluoride will do the job and is
much safer than HF:

SiO2 (s) + 4[NH4][HF2] (aq) †’ SiF4 (l) + 4[NH4]F (aq) + 2H2O (l)
[http://en.wikipedia.org/wiki/Ammonium_bifluoride]

--
Andy