Facts About Glass (for Teachers)
The Art and Science of Glass
Obsidian is naturally occurring glass. It is a product of volcanic activity and was first used in the Stone Age. The material was used for spears and now in heart surgery because of its sharp points.
Glass is made from three substances. Here are the most common:
- Pure silica has a melting point around 2,000 degrees Celsius. The substance alone could be used to make glass, but two other substances are added to simplify the production.
- Soda, sodium carbonate, or potash lowers the melting point to 1,000 degrees C but makes the glass water-soluble.
- Lime, calcium oxide, is added to restore insolubility.
Glassblowing revolutionized the process of making glass objects. By working with glass in a molten state and blowing out a hollow part of the glass, glassmakers could more quickly form objects than they could by using molds and cutting.
It is believed that Mesopotamiams made glass 4,000 years ago.
Properties of Glass
Most glass is transparent, or at least partially so. Most of the light is transmitted through glass. Colored glass is selectively transparent, transmitting light from certain wavelengths or colors.
Light is refracted or bent as it passes through glass. Not all colors of light are refracted in the same way.
At normal temperatures, glass in the solid form is an exellent thermal and electrical insulator.
Terms in Glassblowing
As you explore glassblowing, you’ll discover a complete set of terminology related to the process. Here are a few basic terms.
annealing: a controlled method of cooling glass from the molten state. If glass is cooled too quickly, it may break.
blowpipe: a tool used in glassblowing, made of iron or steel, with a mouthpiece on one end. A ring at the other end helps to gather the molten glass.
gaffer: the person who blows through the blowpipe in glassblowing; in fact, the person who leads the team in the glassblowing process.
gather: a mass of molten glass.
pot: A container made of fire clay placed in the furnace. The molten glass in the pot is gathered by the gaffer.