Donuel,

Another technique for you to try is to gild onto the glass (usually water gilding, but oil gilding can be used to vary the effect) and then 'carve' away the excess, to leave the gold* just where required.
Powdered gold can also be used mixed with a suitable carrier medium.
The gilding can be protected by painting over the back of it.
This gilding, combined with glass painting (as required), is a technique known as Verre Églomisé (I believe it's sometimes known by the German term 'hinterglasmalerei').
There are a number of sites which show the effect, it may be worth considering this as another tool in the box.

Just an idea

Walrus


* Silver can also be used