Fuller’s earth is a naturally occurring absorbent clay, composed mainly of montmorillonite-type minerals, named after the fullers who used it to clean and thicken woollen cloth. Its remarkable adsorptive capacity made it valuable well beyond textiles: in food processing it has been used to bleach and purify edible oils, decolourising them by adsorbing pigments and impurities, and to filter and clarify liquids. It also serves in cosmetics, pharmaceuticals, and as cat litter. In oil refining, the clay is mixed with crude oil, adsorbs colour bodies and oxidation products, and is then filtered out — a classic example of adsorption purification. Modern refineries often use activated clays, but the principle remains the same.