Etching refers to the technique of creating art on the surface of glass by applying acidic, caustic, or abrasive substances. Traditionally this was done after the glass was blown or cast.

Techniques

In the 1920s a new mould-etch process was invented, in which art was etched directly into the mould, so that each cast piece emerged from the mould with the image already on the surface of the glass. This reduced manufacturing costs and, combined with a wider use of colored glass, led to cheap glassware in the 1930s, which later became known as Depression glass. As the types of acids used in this process are extremely hazardous, abrasive methods have gained popularity.

Typically, "glass etching cream" available from art supply stores consists of fluoride compounds, such as sodium fluoride and hydrogen fluoride (very dangerous). The fluoridation of the glass (which is a network covalent solid of silicon dioxide molecules) causes the characteristic rough, translucent qualities of frosted glass.

Abrasive sandblasting is also a common technique for creating patterns in glassware, creating a "frosted" look to the glass. High pressure air mixed with an abrasive material cuts away at the glass surface to create the effect. The longer the stream of air and abrasive material are focused in one spot, the deeper the cut will be. Sandblasting is often used for removing unwanted items that have stuck to the glass or as a decorative purpose on gifted and personal items.

Leptat glass is glass that has been etched using the Leptat acid process. Etched glass has served a unique purpose for hundreds of years, transmitting natural light as clear glass does, while providing a work of art that screens one area from another. Unlike the more typical frosted etch that is produced by an abrasive etching technique, Leptat creates a deeply etched, crystalline surface of varied textures.

Leptat takes its name from the Czech word meaning "to etch", because the technique was inspired by a Czechoslovakian glass exhibit viewed at a past World’s Fair in Osaka, Japan, and patented in the US by Bernard E. Gruenke, Jr. of the Conrad Schmitt Studios. Abstract, figural, contemporary and traditional designs have been executed in Leptat glass. A secondary design or pattern is sometimes etched more lightly into the negative areas, for further interest. Gold leaf or colored enamels also can be inlaid to highlight the designs. The Leptat technique allows the glass to reflect light from many surfaces, like a jewel-cut gem.

Glass etching can also be done using hydrofluorosilic acid (H2F6Si).