This London from The Thames 'Scape is created using sheet and powder glass together with copper oxide.  
 
I sketched the London scene over the Thames using a 'waxy' brush on the reverse of a sheet of glass.  Then carefully dusted the sketch with the copper oxide powder removing off any excess powder.   This piece of glass was then placed onto a an opal sheet of glass onto which I had sieved glass powders in fiery reds and oranges.   
 
During the firing in the kiln, the copper oxide reacts with the red and orange powders creating the fine dark bubbles that create the sketch lines.
 
Approx 15cm x 10cm.  Displayed in the image on a small wooden tripod stand.