Etching refers to the technique of creating art on the surface of glass by applying acidic, caustic, or abrasive substances. Traditionally this is done after glass is blown or cast, although mould-etching has replaced some forms of surface etching.
Various techniques are used to achieve an etched surface in glass, whether for artistic effect, or simply to create a translucent surface.
Acid etching is done using hydrofluorosilic acid (H2SiF6) which, when anhydrous, is colourless. The acid is prepared by dissolving silica in a mixture of hydrofluoric acid, quartz powder, calcium fluoride and concentrated sulfuric acid derived after heating.
Glass etching cream is used by hobbyists as it is generally easier to use then acid. Available from art supply stores, it consists of fluoride compounds, such as sodium fluoride and hydrogen fluoride (which are still very dangerous). The fluoridation of the glass causes the characteristic rough, translucent qualities of frosted glass.
Mould etching In the 1920s a 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.
Abrasive sandblasting is another common technique for creating patterns in glassware, creating a "frosted" look to the glass. It is often used commercially. High pressure air mixed with an abrasive material cuts away at the glass surface to create the desired effect. The longer the stream of air and abrasive material are focused in one spot, the deeper the cut will be.
Leptat glass is glass that has been etched using a patented acid process. 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 United States 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.
- Leptat Glass, GoHistoric.com
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