subject: The Chemistry of Glass and Glassmaking [print this page] The Chemistry of Glass and Glassmaking The Chemistry of Glass and Glassmaking
You might have thought that nothing from your high school chemistry class would be of use after graduation. But surprisingly, chemistry plays an important part in creating beautiful glass.
Glass is more closely related to Chemistry than one might think; much credit goes to chemists who have discovered elements that can enhance certain aspects of glass, and also improved colors.
Glass is not a naturally occurring substance basically the cavemen had to wait until a volcano erupted or a lightning struck until they could find some glass. Hence glass today is created artificially, sometimes in factories and sometimes in the private studio of an artist with his or her own glass formula.
There are two essential elements that go into making glass: silica (sand, quartz, flint) and alkali (soda, potash). Alkali melts silica, so that the two can combine easily.
Silica is the most important ingredient, taking up about 60-70%. Venetians traditionally crushed white quartz pebbles, and the English burnt flints for silica. The freer the silica is from impurities, the better. When unrefined silica was used to make glass, the color would turn out to be dark green or brown, which is seen in early glassware and the least expensive types of glassware. But if one wanted to create fine glass, sand had to be washed and heated carefully.
The rest of the glass consists of up to 20% alkali flux. Traditionally, plants and trees were burnt to obtain it. Soda and potash continue to be used in glassmaking even today.
Other ingredients are sometimes added for various purposes:
Lime: For stability. Using lime will produce light and inexpensive glass, used for bottles, window panes, and light bulbs.
Magnesium: to counter the effects of impurities in the sand. It makes glass clear and colorless.
Lead oxide: For weight and brilliance. George Ravenscroft developed the use of lead oxide in 1674 in England, with which he made durable, brilliant, and weighty glass that could sustain deep cuts. The addition of lead oxide literally changed the history of glass and trade because after its appearance the Venetian cristallo lost some of its allure.
Metal oxides: for various colors, be it red, blue, or green. Will be covered in more detail in a later article.
When the proportions of chemical elements are not right, glass might appear "crizzled." Hence understanding chemistry and the combination and interaction of elements are a very important part in creating high quality glass work.
