or **Trituration**, the act of breaking or comminuting a solid body, and reducing it into powder. See **Pulverisation** and **Levigation**.

The painters colours are ground on a marble or porphyry, either with oil or gum-water.

Grinding is also used for rubbing or wearing off the irregular parts of the surface of a body, and reducing it to the defined figure, whether that be flat, concave, or the like.

The grinding and polishing of glasses is a considerable art; for which see **Glass Grinding**. For the grinding of optical glasses, see **Optics**, the Mechanical Part.