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!