stained glass with painting

Glass paints (low-melting lead-boron glass with coloring ingredients) are ground to a very fine powder which is diluted with turpentine and other binders for painting. The colors are fired in an electric furnace at temperatures of about 560°C.
Other option are more modern organic colors, the so-called hydro-glazes, dried at 180°C.
Painting on glass requires considerable skill and experience.