Etching glass II

A small piece of window glass was uniformly frosted with 45 micron diamond powder made into a paste with glycerine (using a flat glass muller) then washed and dried. The reverse was masked with Sellotape, and a design painted on the front with nail varnish. After thorough drying, it was re-etched by immersion in 15% sulphuric acid with about 10% sodium bifluoride added, in a sealed plastic container for about 24 hours.
The results after this time were disappointing, with no apparent change in the frosting when wet. After washing and drying, again there seemed little change in the frosting - at least for the first few minutes! After that, to my astonishment, a dendritic growth of what seemed to be white crystalline material appeared over the whole of the exposed glass surface, taking about 5 minutes to cover it entirely. On scraping with a blunt plastic tool, it was found to be some kind of loose surface material, presumably silica-based. It was again washed, and the masking agents removed. This plainly showed a difference in the etching texture given by diamond paste compared with the chemical etch. I need to research the nature of silica degradation by bifluoride!

Etching glass I

I like equally the effect of both etched metal and etched glass. But the latter requires use of hydrofluoric acid or equivalents, which is not fun to use at all. It demands a fume cupboard and a professional approach to personal protection equipment.
So I have been experimenting with a potentially safer alternative, namely bifluoride salts. Unfortunately I have not been able to find a supplier of ammonium bifluoride, the salt of choice because of its high solubility in water. Instead I have to make do with sodium bifluoride, which has very limited solubility.
My present interest is in 'bite & grind' which refers to etching a design onto sheet glass, and grinding the design in selected areas with a flat glass pad loaded with diamond abrasive and glycerine as a lubricant. Sometimes one might use 'grind & bite' instead.
Work is going slowly at the moment since this is the middle of the spring term and most of my time is taken up with teaching and administration; and early next week is scheduled as the 'casting days' for two different classes, using silicon bronze, silver and pewter depending on the students' interest.