The ceramic rods are made of "high alumina" ceramic. This material is extremely wear resistant, while having remarkable "cutting" properties and will not wear out under normal use. During sharpening, your ceramic rods will develop a residue buildup from fine metal shavings. Rotate the rods to expose a clean surface. To restore the full abrasiveness to the ceramic rods, clean with Idahone's "Supereraser" fibrous block, or use an ordinary household abrasive cleanser.