Natural glass, like obsidian, is a dense volcanic glass, and has been used by man for millennia. To early man, obsidian glass was an extremely rare and valuable commodity, because of the way volcanic glass fractures, sharp edges occur. This inherent quality of natural cut glass was put to use and was often made into sharp spear points and blades.
Man-made rudimentary glass was made from silica sand, plant ash and lime. Over time it was discovered that if glass was heated until it became 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 first century BC, the craft of melting and blowing glass into useable objects was 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 purpose and daily use.
Common glass normally has a greenish hue. The green tint is caused by minuscule amounts 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. Colored glass of reds, blues and greens become 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.
Around 1000 AD, a new development was made in glassmaking. The glass making component of soda-lime, was replaced by potash obtained from wood ashes. From this time on, glass from the northern part of Europe differed very much from that made in the Mediterranean area, where soda-lime remained in common use. Centuries later in Bohemia, ashes from beech trees were used. The production of Bohemian "forest glass" was progressively refined over the years.
During the 11th century new ways of making sheet glass came about in Germany. Glass blowers would blow spheres, and then form them into cylinders. They would cut the glass while still hot and then flatten the glass into sheets. Glass makers in Venice, Italy improved this method in 13th century. By the late 1300's there was as many as 20 glassworks in Bohemia and Moravia. The 12th century saw the arrival of stained glass production. Stained glass, another form of colored glass, was made by adding metal impurities. Church and monastery applications of stained glass can be traced back to examples that remain today, ie St. George. Bartholomew church in Kolin. A glass wall mosaic is preserved there from around 1380.
Venice became the dominant center for glassmaking during the 14th century. Here new glass making methods were developed and export trade such as mirrors, tableware, and decanters flourished. Secrets of glass making were highly guarded in Venice, but historically glass workers moved to other areas of Europe taking their knowledge and skill with them.
A technique called "the Crown glass process" was used to make glass until the mid part of the 1800s. A glassblower would spin around 9 lbs of molten glass at the end of a rod until it spread out into a flat disk nearly 5 feet across. The glass disk would then be cut into panes. Glass from Venice was highly prized for over four centuries as they managed to keep this technique secret. In 1688, a method for casting glass was invented. This led to glass and glass panes in becoming a much more common material. The glass pressing machine was invented in 1827 and facilitated mass production of relatively inexpensive glass items. The glass pioneer, William J. Blenko, is recognized as first glass producer in America to use the cylinder method of creating flat glass by the 1920s.
The Bohemian countries of Czech and Slovakia are still known today as two of the finest cut glass and cut crystal producers in the world.