Natural glass, like obsidian, is a dense volcanic glass and has been used by humans for thousands of years. For early humans, obsidian glass is a very rare commodity and precious because of the way volcanic glass breaks, sharp edges occur. This inherent quality of natural cut glass is utilized and often made into sharp spear points and knives.
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The man-made glass base is made from silica sand, plant ash, and lime. Over time it was discovered that if the glass is heated until it becomes semi-liquid, it may be molded or shaped and left to cool into a solid new piece or vessel. In ancient times glass pieces were valued as a substitute for precious stones or gems.
During the first century BC, the craft melting and blowing glass into objects that can be used are developed. Glass pieces and items gradually became more common after the discovery of glassblowing. Objects such as vases, bottles, and cruets were mouth-blown and mold-blown during the Roman Empire, usually for ordinary purposes and daily use.
Common glass usually has a greenish hue. The green color is caused by a very small amount of iron impurities in the sand used to make glass. Glass producers learned to make decorative and colored glass by adding metallic compounds and mineral oxides such as cobalt.
A glass of red, blue and green color becomes prevalent. After craftsmen learned to score and cut glass, they found clear glass refracted light in spectacular fashion. Thus, clear cut glass became popular, and demand for colored glass plummeted.