Fine sand, mineral oxide.  Colorant and a texturizing agent in glazes and clay bodies. 
Promotes Iron spotting in reduction.  Produces tan and buff in oxidation.
 
Ilmenite is primarily used to produce specific visual effects: 
Speckling: When added in granular form to a clay body or glaze, ilmenite creates dark brown or black specks. The size and number of the specks depend on the granularity of the ilmenite and the quantity used.
 
Coloration: It contributes to dark colors, such as browns and blacks, in the fired ceramic piece.
 
Variegation/Crystallization: Ilmenite can be used to "seed" or promote crystal growth and variegation in certain glazes, especially those fired in a reduction atmosphere or specific crystalline glazes.
 
Texture: Its refractory nature and granular form add physical texture to the surface of the pottery. 
Ilmenite is considered an important raw material for artistic ceramics, providing unique and often unpredictable natural patterns that mimic the look of oxidized metals or stones.