Spray A Plus surface primer is a clear, low melting glass, ground to micron size and suspended in a spray medium. It is applied to glass by brushing on or spraying prior to firing to prevent devitrification on the glass surface. It may also be used as an overglaze for dull or matte surfaces or even previously devitrified surfaces. Fire to a minimum of 1300 degrees F (704 degrees C). 16 oz bottle.