In this example piece shown, the glass was airbrushed with sufficient paint that light could not be seen through the glass when held up to a window.
We mixed the paint with Color Line air brush medium, two parts paint to one part medium.
The piece was then air dried for about 30h (this time can be shortened in a drying cabinet). The glass was placed in a Paragon GL24 on a shelf which had been prepared with Bullseye shelf primer. The kiln was slowly fired to 500°C (930°F) in about three to four hours. The door always open about 2.5cm (1") and the bung removed. Then held at this temperature (doors and bung still open) for 15 min. After this the door was opened fully for a few seconds, then closed and continued firing to 780°C (1436°F) in about one hour.
It is very important that the fumes from the burning out of the medium have been exhausted from the kiln before the higher temperatures are reached. To obtain a good red you need a well oxygenated atmosphere. Any carbon residue will create a reduction atmosphere in the kiln giving inconsistent results.