The Art of Blowing Glass
What is glassblowing?
Glassblowing is a technique used by a person (called a glassblower or gaffer) who blows air into a steel blow pipe (usually about 6 feet long) that has molten glass gathered onto the opposite end. The air produces a bubble inside the glass thereby inflating the glass. From this point forward, the gaffer is able to shape the glass into its final form.
Where does the molten glass come from?
Glass is formed by melting natural raw materials together inside a crucible which is a large ceramic pot that rests inside of a furnace. These raw materials usually include but are not limited to silicon dioxide, sodium carbonate and calcium. They are melted in the furnace at a temperature around 2100-degrees F. The furnace is maintained at a temperature of around 2000-degrees 24 hours a day, 7 days a week so as to keep the glass molten at all times. (Allowing the glass to cool and harden and then re-melting it over and over would cause too much stress on the crucible inside the furnace causing it to crack.)
What happens after the bubble is formed?
At this point, the gaffer uses different tools and techniques to shape the glass while working at a bench. Molds, blocks, marver tables and other tools may be used as well depending on the design intended. At this point, the gaffer is typically working the “bottom” of the piece.
Proper heat must be maintained so the piece will not fracture so the gaffer or the assistant will reheat the piece in a 2400-degree “gloryhole” as needed.
Because molten glass has a consistency similar to honey, it is crucial that the blowpipe is rotated continuously throughout this entire process.
About halfway through the process, the piece is typically transferred to a punty which is a solid steel rod (no hole down the center like the blowpipe). This step is crucial and challenging as the proper maintenance of heat in all the proper places of the piece make a difference as to whether the piece will make it or break. But once the piece is off the blowpipe and onto the punty, the gaffer is then able to complete the “top” of the piece.
How do they get the color in the piece?
Color is achieved by using different metal oxides. For instance, cobalt will usually result in blues while gold produces varying shades of reds. Color in glass is a challenge because the amount of oxygen, the types of metal oxides and even the order the oxides are applied can all form different colors. And the same methods used can still result in different outcomes.
Glass rods of solid colors can be melted into the clear glass, shards (or frits) of colored glass can be laid or rolled in or powders can be sprinkled on or rolled in.
What happens when the piece is finished?
Once the gaffer has completed the piece, it must be removed from the punty (steel rod) and then annealed. The gaffer will gently tap the rod to break the piece off the punty. Sometimes, if the mark has not been polished away, you can see and/or feel a “punty mark” at the bottom of a glassblown piece. That is the point where the gaffer detached the piece from the punty.
If hot glass is left out at room temperature, it will most likely explode or, at minimum, crack due to the extreme temperature changes. An annealer is like an oven. It is kept at about 950-degrees F throughout the day. All finished pieces are placed into the annealer. At the end of the day, the annealer is set to automatically and systematically cycle down to room temperature. This typically takes 8-12 hours for standard bowls, vases, etc but can take up to days and weeks for larger or more dense pieces.
The final stage of completion is called cold-working. This is a series of techniques that may be used on the piece once it has reached room temperature. Most of these techniques require diamond-bitted tools to complete. Examples of cold-working are grinding, polishing, sandblasting, engraving or even the artist signing the piece.