Answered By: Rebecca Hopman Last Updated: Dec 18, 2016 Views: 304
Great question! Most glass is made of silica (sand), lime, and soda ash. These ingredients have natural impurities (like iron oxide), so they produce a greenish glass. Glassmakers have been adding chemicals to glass since Roman times to try and make clear glass, but it wasn't until the 15th century that they were able to develop a dependable formula. In the late 1400s, glassmakers in Venice, Italy developed a perfectly clear type of glass called cristallo. They used quartz sand and potash to make the glass. This glass was prized because it was so clear, which might seem strange to us, as clear glass is so common today. The development of clear glass led to the invention of important technology like magnifying lenses and reading glasses. Later on, in 1674, a man named George Ravenscroft invented a type of glass known as lead crystal. He added lead oxide to his glass recipe to make brilliant colorless glass. This glass was often cut with complex geometric patterns to make the glass sparkle like real gemstones. Today clear glass is pretty common, but it took many hundreds of years before glass was both clear and cheap enough for average people to buy!
See the attached bibliographies for books and websites about glass written for kids and teens. You may be able to find these books at your local public library. If not, you may be able to borrow them from us. We participate in a worldwide service called the Online Computer Library Center (OCLC). Your library can contact us through OCLC or they may send an Interlibrary Loan form to us by e-mail. We loan certain books if a second copy is available in the library collection. Books are loaned for a four week period. For further information, please see our web page: http://www.cmog.org/research/library/visit/services/loan.
- Sand, the major ingredient in glass contains iron as an impurity. tHis imparts the common green color seen in "Coke" bottles and window glass when viewed on its edge. The glass appears green in transmission because the red and blue components of light are absorbed by the iron. Glass manufactures then add small amounts of cobalt and selenium to absorb the green components resulting in a slight but equal absorption of all colors, thus the glass appears clear as all colors are equally absorbed. The over all transmission drops slightly, but the glass looks clear.