Rutile Ceramic Powder

Only a small amount of ceramic rutile dissolves in a glaze melt. The excess separates out again as the kiln cools, seeding crystals through the glaze and splitting the melt into two intermingled glasses. Light scatters where those glasses meet, so a rutile glaze breaks a colour into streaks, mottles and cloudy pools instead of tinting it evenly. On its own it gives ivory, butter yellow and tan in oxidation, and purple and blue in reduction, though it is usually added to move another colourant around. It supplies minimal flux, so a heavy addition stiffens a glaze and mattes it. The ore is mined, so there is some variation from lot to lot, and a test of a new lot before a full batch is good practice.