Quartz / Silica

Quartz, chemically pure silicon dioxide (SiO2), is the fundamental glass-forming material in ceramics. It is the second most abundant mineral in Earth’s crust and the backbone of every glaze and most clay bodies.

On its own, quartz melts at over 1,700 degrees Celsius, far above any potter’s kiln. In glazes, it only becomes glass when combined with fluxes (like feldspar, limestone, or zinc), which chemically break down the silica structure and allow it to melt at reachable temperatures. The flux-to-silica ratio in a glaze is the single most important variable affecting its final character.

Higher silica glazes are harder, more durable, more chemically resistant, and less prone to crazing. Lower silica glazes melt earlier and run more. Nearly every glaze recipe calls for additional quartz beyond what the feldspars contribute, to fine-tune the final silica content.

Silica also plays a critical role in clay bodies, where it provides structural strength and helps match the glaze to the clay (thermal expansion matching reduces crazing and shivering).

Typical usage: 15 to 35 percent in most glaze recipes. In clay bodies, 15 to 30 percent as a filler for porcelain and stoneware.

Safety note: Silica dust is harmful if inhaled over time. Always wear a dust mask when handling dry powders and work in a ventilated area.