Engraving is the removal of material from the surface of an object (coin die, gemstone, glass, etc.) using variously shaped stone and metal wheels and drills, and an abrasive powder.
Free-hand glass engraving is also known as scratching. When wheel-cutting the artisan holds the vessel at various angles against the edge of a fixed turning wheel to cut the desired pattern. The shape of the wheel's edge determines the shape of the cut. The most common form of wheel-cutting is a series of decorative horizontal grooves. Wheel-abrading was used to create flat surfaces. Facet-cutting, intaglio and figural engraving were the work of highly-skilled specialized artisans. It is not unusual to see more than one technique on a single glass piece.