High temperature glass painting is an ancient technique and has changed little over the centuries. It is still used a great deal today to enrich stained glass windows with images which would not be possible just using coloured glass. Once you have found the painting you wish to see on the glass, you sketch an outline with a brush using the appropriate powder mixed with a fatty substance. Once this has dried, a light layer of grisaille is placed on it to create the chiaroscuro effect. If the pane needs further colour one can use enamels.
The whole glass painting is then fired in a kiln at around 600°c, rendering it permanent and indelible.