This is a reverse glass painting.
It's painted on the *back* of the glass in reverse order. That is, highlights go on first, and the background goes on last.
If you make a mistake, there is no way to go back and fix it!
The result is a painting with an incredible gloss.
Transperant acrylics on 3mm glass.
A4.
Here is the pencil sketch that I worked from.