Flint glass refers to a type of optical glass recognized for its high transparency and refractive value. The origin of flint glass took place in the 1600s, when powdered flint became an additive used to improve the quality of blown glass. It is also a name for certain types of pressed glass dishware made throughout England and the United States between 1820 and 1865.
The first true flint glass was developed in 1662 by English glassmaker and businessman George Ravenscroft. He used particles of flint to produce a particularly refractive and refined type of glass. Flint glass became the standard of excellence in glassmaking technology until it was discovered that lead added to the silica mixture produced a far superior glass. Although it is more properly called lead glass, the name “flint glass” remains in common use.
Modern industry uses flint glass primarily to make optical lenses. Optical glass has many scientific and military uses, such as binoculars, gun sights, telescopes, periscopes, and microscopes. There are several grades of optical glass available, depending on the desired specifications. Considerations can include thermal properties, expansion rates, mechanical properties, refractive properties, and optical clarity.
For antique collectors, flint glass means dishware collectibles, also called lead glass, leaded glass, lacy glass, or pressed glass. From 1820 to 1865, glassware was produced by pressing the softened silica mixture into patterned molds. The molds provided ample latitude for intricate designs, dubbed as “lacy” when compared to earlier hand-blown glassware. When lead became scarce during the American Civil War, further developments in patterned glass evolved. A method called lime glass is considered the preferred formula today.
Lead glass collectibles can fetch a hefty price, especially for rare designs. Authentic period plates, saucers, cups, pitchers, bowls and platters can range from $20 to $3,000 US Dollars apiece. Antique collectors look for patterns described as horn of plenty, honeycomb, bellflower, Hamilton, and cable, among others. Collectors will also test for a bell-like ring in the glass that is only present in the finest pieces. A small crack or blemish will usually diminish the tone of the ring, and lower the value of the piece considerably.
A sampling of flint glassware can include transparent or translucent pieces, as well as opaque pieces in any color. Edges can be scalloped or smooth, and designs can include flowers, birds, grape leaves, historical dates, public buildings, and commemorative sayings. Another popular design incorporates geometric shapes made of simulated cut glass crystals.
There are several glassware manufacturers, such as Waterford®, that still produce authentic lead crystal glasses. Lead content can range from 24 to 33 percent. The lead adds heft and optical clarity that is unsurpassed, forming an unbreakable chemical bond that cannot contaminate food or drink. Like the original glassblowers of the past, the makers of lead crystal glassware strive to make perfectly formed glassware of the highest optical purity.