Glassblowing Furnace: Time for the Cool Down
Once a piece of glass is complete, to help it cool properly, an annealer is used. The third furnace in the series, the annealer has a very important job. This stems from the fact that glass, remember, is an amorphous solid. As the glass cools it may naturally start to crystallize -- but that's not a good thing, because that means the glass has lost the properties that made it so useful and special to begin with. The goal is for the glass to cool and retain its scattered but rigid molecular structure. As this happens, it contracts and loses more and more of its viscosity until it becomes solid glass.
So to ease our newly blown piece of glass through this process, an annealer (sometimes called a lehr) is used to control the rate of cooling. Otherwise, the glass could suffer thermal shock and become unstable. A pyrometer carefully measures the temperature during the annealing process while the glass is brought below the point of softening and is carefully cooled over an extended period of time. This helps get rid of any internal strain or tension in the blown glass, so it's less likely to break down the line. The size and dimensions of the piece affect the length and rate of cooling.
Last but not least, the nearly finished piece of blown glass is often taken to the cold shop where it can be ground, polished, engraved, enameled and otherwise detailed. Glass etching and relief sculpture are just two of many ways glassblowers can increase the craftsmanship in their blown glass art.
Blowing glass is challenging work, and there can be a lot of risks involved. Glass can crack and explode if it not worked properly -- and let's not forget about burns. Plus, a lot of the ingredients in a glass batch are either toxic or if airborne, can cause respiratory problems over time. To counteract these dangers, glassblowers wear protective clothing, safety glasses, respirators and face shields to defend them against injury and exposure -- as well as the ferocious heat pouring out of the furnaces.
Now that we've seen what goes in to glassblowing, let's check out how you can join the ranks of the world's best.