The firing of enamels onto borosilicate glass through the selective absorption of infrared radiation

Abstract

Gradations and other markings on laboratory glassware are made mainly with glass enamels. Firing temperatures of around 600 °C (i.e. 70 to 80 Κ above the transformation temperature of the glass) are needed in order to reach sufficient chemical and mechanical resistance. This can lead to alterations in the volume of the flasks. Due to the uneven temperature distribution in continuous or batch furnaces some flasks may undergo a volume change that is greater than the accepted margin of error of the calibration. The aim of this study was to find a firing process for glass enamels that ensures the same chemical resistance as the furnace firing but without the risk of changing the volume. This was obtained by a combination of conventional heating by a hot-air blower and selective heating by absorption of infrared radiation. A halogen lamp and an Nd-YAG laser were used as infra-red sources. The use of the laser clearly showed better results. By firing-on blue lead-enamel with a laser a chemical and mechanical resistance comparable to that of furnace firing was achieved without altering the volume of the measuring Container.