Q. What makes some glass clear or colorless?

History of Clear Glass

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, because clear glass is so common today.

Some Uses of Clear Glass

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!

Learn More

A number of books exist for young people to learn more about the history and science of glass. A few recent examples are listed here, but you can view more titles in the Rakow Research Library catalog or ask us to send you a reading list!

• Graham, Ian, and Bergin, Mark. You Wouldn’t Want to Live Without Glass! New York: Franklin Watts, an imprint of Scholastic Inc., 2017.
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• Koscielniak, Bruce. Looking at Glass through the Ages. Boston: Houghton Mifflin Co., 2006.
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• Langley, Andrew. Glass. New York, NY: Crabtree Pub. Co., 2009.
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• Somervill, Barbara A. The Story Behind Glass. Chicago, Ill: Heinemann Library, 2012.
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• Stevens, Beth Dvergsten. Glass: From Beads to Bottles to Windowpanes. Logan, Iowa: Perfection Learning, 2004.
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• Stewart, Melissa. How Does Sand Become Glass? Chicago, Ill: Raintree, 2010.
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Borrowing Library Materials

You may be able to find these books at your local public library. If not, you may be able to borrow them from us through Interlibrary Loan (ILL) at your local library. For further information about ILL policies and procedures, please see our Interlibrary Loan page.