Glassblowing is a glassforming technique that involves inflating molten glass into a bubble (or parison) with the aid of a blowpipe (or blow tube). A person who blows glass is called a glassblower, glassmith, or gaffer.
Glass is made up of silica, which is basically a high-quality type of sand. Other materials, such as metals and metal oxides, are added to silica to lower the melting point of the mixture. Other key ingredients often found in glass include soda (sodium dioxide) and lime (calcium oxide).
Glassblowers mix these ingredients to make a batch of glass, which they will melt in a furnace in their workshop (called a hot shop). The batch is heated in a pot called a crucible to an initial temperature of over 2,000º F.
While glass can be blown by one person alone, it’s a challenging task that’s usually best tackled by a team. The lead glassblower is called the gaffer. The gaffer uses a blowpipe (a hollow tube made of iron or steel that’s usually about four feet long) to dip into the crucible to coat the end with a blob of molten glass.
The gaffer then blows into the blowpipe to create a bubble in the molten glass. Depending upon what kind of product the gaffer wants to make, a large, flat surface called a marver can be used to shape the glass. Other tools, including blocks, jacks, heat shields, and paddles, help the gaffer and his team to shape the molten glass into the final product desired.
As the glass is being shaped, it often cools to the point where it becomes unworkable. When that happens, the glass must be put into a second furnace (called the glory hole) to reheat it to the point where it’s once again flexible enough to shape further.
When the glass product is finished, it must be cooled carefully. A third furnace, called an annealer, is used to slowly cool the glass product to the point where it becomes a sturdy solid that’s still transparent. If glass is cooled too quickly, it can crystallize and lose its transparency while also becoming extremely fragile and subject to breaking easily.
Free demonstrations at various times on the Upper Grounds.