Britannica Sources used in this answer

How does feldspar lower the firing temperature of whiteware?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

traditional ceramics Stages in the slip casting of a thin-walled whiteware container. Clay powder is mixed in water together with a dispersing agent, which keeps the clay particles suspended evenly throughout the clay-water slurry, or slip. The slip is poured into a plaster mold, where water is drawn out by capillary action and a cast is formed by the deposition of clay particles on the inner surfaces of the mold. The remaining slip is drained, and the cast is allowed to dry partially before the drain hole is plugged and the mold separated. The unfinished ware is given a final drying in an oven before it is fired into a finished product.

In the production of whiteware, feldspar functions as a fluxing agent, which is a substance used to reduce the melting temperatures of the aluminosilicate phases within the ceramic mixture.12

By acting as a flux, feldspar facilitates the process of vitrification—the formation of glass—at lower temperatures than would be required for the other raw materials alone. During the firing process, feldspar grains begin to form a liquid phase at temperatures as low as 990 °C (1,810 °F). This liquid phase promotes the consolidation of the ceramic body through liquid-phase sintering, where the viscous flow of the glass helps rearrange particles and fill pores, ultimately leading to the densification and strengthening of the final product.132

Because feldspar lowers the temperature at which this glassy liquid forms, it allows manufacturers to achieve the desired degree of vitrification and structural integrity without needing to reach the significantly higher melting points of pure silica or alumina.23