Temperature Assessment Through Decal Color in Microwave-Fired Porcelain

Porcelain ware typically undergoes multiple firing stages, including decoration firing at temperatures that depend on the desired effect. Conventional decorative firing in gas tunnel kilns takes up to 90 min, whereas microwave heating offers a faster alternative, of around 50 min firings for both low- (~800 °C) and high-fire colors (~1200 °C). However, temperature assessment during microwave firing remains challenging. This study investigates the color changes in overglaze-decorated hard microwave and conventional porcelain firing. Decals with temperature-sensitive pigments (silver and blue) were applied to the porcelain pieces. Color coordinates (L*, a*, b*) were analyzed, comparing microwave and electrically fired samples with the gas-fired reference counterparts. Microwave-fired samples required lower temperatures to match the color of electrically fired samples. Electrically fired pieces at 900 °C are visually comparable to those processed in both a microwave furnace and a gas kiln at the same temperature of 800 °C. Color differences among different heating methods decrease as firing temperature increases. Microwave firing allows similar decorative results to be achieved as with conventional gas firing, while being faster and more energy efficient. Microwave porcelain firing is thus a viable and eco-friendly alternative for porcelain decoration, and the decals’ color changes can be used for temperature assessment during firing.