A reactive glaze is often used in ceramic and does not have a homogeneous solid color or character. These kinds of glazes are also known as variegated or mottled.
These mottled glazes are highly prized by some ceramists because of the unusual variations of color and texture that can be created in each piece. To create the variegation, special agents are used in the glaze. Those agents may include crystal growth, speckling agents, layering, thickness variations, translucent glazes and phase separation.
According to Spectrum Glazes, some types of reactive glazes are rated as C/L by the ACMI. That means the glazes are considered to be toxic when they are still in their liquid forms and have been unfired. There may be heavy metals, such as vanadium or copper, in the liquid glaze, and they can be beyond the nontoxic legal limit. Because of the potential toxicity, C/L-rated glazes are unable to be used by pregnant women or younger children.
Popular uses for the reactive glazes include stoneware. The reactive colors create multitonal and multicolored effects due to the metal oxides in the liquid mix. These glazes can be layered to create unique looks, making them prized among the ceramics community.