Glassblowing: A Process of ‘Happy Accidents’
Glassblowing has been a process of ‘happy accidents’ from the time it was rumored to be discovered by shipwrecked Phoenician sailors around 23-79 A.D. along the Mediterranean coastline that stretches across present-day Syria. The sailors started fires on the beach that exceeded 1800° C -- hot enough to fuse the grains of sand into silica glass.
That knowledge made its way to Europe and the craft of glassblowing was formalized in 1st Century B.C. in Cologne, Germany and some would say the craft was perfected by the Venetians during the Renaissance period. Since then, the delicate art of glassblowing has come in and out of vogue throughout the centuries.
Modern Day Glass Blowing
Tradecraft is making a comeback in a big way with an increasing number of young people studying to be butchers, woodworkers, and bakers: old world crafts that were phased out by machines are now coming back in style with a focus on “small batch” and “handcrafted” items.
Glass artists, such as Seattle-based Dale Chihuly, gained notoriety in the late ‘80s and ‘90s and created a renewed interest and Renaissance of sorts for glassblowing. If you run a quick search online today, you are likely to find dozens of glassblowing classes and courses offered at local studios if you live in a metropolitan area.
Visiting a Glassblowing Studio: What To Expect
If you are considering learning the craft of glassblowing, what can you expect from your first visit to a studio? Expect the glassblowing studio to be hot. Exceptionally hot. The furnace you will be working with exceeds 1,320° C.
Tips for first-time visits to a glass studio:
Do not stand in front of the furnace longer than necessary. The heat is intense and prolonged exposure, especially without tolerance, could make you lightheaded.
Hydrate before your class and bring a large water bottle so you can stay hydrated throughout a long, hot lesson.
You will be working with molten glass so it is very important to keep your skin covered. Given the extreme temperatures, opt for lighter fabrics such as a long-sleeved cotton shirt. Avoid synthetic fabrics that are prone to melting in high heat.
Similarly, it is important to wear closed-toed, durable, slip-resistant shoes. Other classmates may unintentionally spill graphite powder and you don’t want to slip while holding “cool” glass -- cool glass is still 482° C!
If you have long hair, keep it tied back and tucked away.
It’s important to wear protective eye gear, but sunglasses would also be helpful for your time spent in front of the furnace.
Glassblowing Equipment and Terminology
Like many other crafts, glassblowing comes with a specific toolset and terminology that you will have to learn in order to become a master.
Gaffer: The lead glassblower. While glassblowing can be done individually, it’s such a challenging process that it is often done with an assistant or even a team of assistants.
Glory Hole: The casual term used to reference the furnace.
Blowpipe: An iron or steel pipe that measures roughly 1.2 meters in length, used to blow air from the gaffer’s mouth into the ball of glass to begin creating a bubble.
Gathering Iron: An iron rod used to gather molten glass after it has been brought out of the furnace.
Marver: A large flat surface used to roll and shape the glass.
Block: A wetted wooden shaping tool, as is a bladed tool called a jack.
Paddle: A tool that is used to smooth out the glass and sometimes to shield the gaffer from the extreme heat of the glory hole.
Tweezers: Another useful tool for grabbing and manipulating hot glass.
Parison: Term for partially blown glass.
Punty: A smaller metal rod often used to add bits of glass to the parison (as various colorants).
Threads and Wraps: Terms used to describe the stretched parison that is used to create decorative patterns on the glass object being created.
Pontil: Another metal rod and tool that is attached to the base of the blown glass to hold it while the mouth end is being shaped. The mark that the pontil leaves in the parison is typically polished off later.
Yokes: Metal stands inside the glory hole where the partially blown glass rests until it is hot enough to continue the process.
Annealer or Lehr: A specific furnace that controls the rate of cooling to keep the finished piece from cracking.
Pyrometer: Measures the temperature during the annealing process to ensure that the glass is brought below the point of softening.
Cold Shop: Term used to describe a studio apart from the glass blowing studio (without furnaces) where it is ground, polished, engraved, or enameled.
About the Sand
Glass is a solid and yet it’s transparent. This is due to the unique molecular structure of glass which makes it more similar to a liquid than a solid. It is this unique molecular structure that allows for glass to be blown into shapes like bubbles, yet molded like clay.
Most of the glass that you will encounter is an oxide glass and the base is silica (silicon dioxide) or sand. This isn’t Syria in 23 A.D., so the sand being used is no longer the sand you pick up by the bucketful at the beach. Rather it’s a sand that has been cleaned of impurities or contaminants, to increase the control that the gaffer has over the glassblowing process.
The sand is mixed with fluxes, which lower the melting point of the sand and increase the flow rate of the glass mixture. Fluxes include alumina, zinc oxide, barium oxide, and lithium. Once the glass is mixed into batches, you’re ready to begin.
Charging the Batches
The gaffer, or the assistants, will place a batch inside a pot inside of the glory hole. In a process called charging, these batches melt at 1,100° C. The gaffer will reach for his blowpipe and dip it into one of the charged batches. The gaffer constantly spins the blowpipe in a controlled manner and the glass is secured to the end. The opposite end of the blowpipe, where the gaffer will blow, is cooled off in a barrel of water.
When the blowpipe has been sufficiently cooled, the gaffer will blow through the tube and create a bubble in the glass secured at the opposite end. Whenever he is not blowing, the end of the tube is capped so the hot air remains trapped in the glass, maintaining its shape.
It is important not to inhale when your lips are on the blowpipe during the process of glassblowing. The air inside is heated at several hundred degrees and while the length of the pipe might allow it to cool to a more tolerable temperature before it reaches your lips, it’s better to be cautious.
When observing the gaffer in a glassblowing class, pay close attention to where he places his hands are on the blowpipe. Glass blowing is about control and proper hand placement on the blowpipe is key to maintaining balance and control over your piece.
More layers of glass are sometimes added with the gathering iron, or by dipping the glass that is attached to the blowpipe back into the batch. Gaffers will often make several trips to the glory hole to add glass and maintain the heat while they work.
Coloring and Shaping Molten Glass
To add color, the parison is spun constantly by the gaffer while he or an assistant add bits of glass with the punty to add color. The gaffer will use a marver, block, bladed jack, or paddles to roll and shape the glass into its desired form. Tweezers are used for more detailed work and to manipulate smaller glass pieces. Glass threads and wraps are added from the batches to create patterns if desired.
Transferring the Parison to the Punty
One of the main reasons why glassblowing is often done by a team of people is because of the transfer to the punty. The parison will be transferred to the same rod that was used to strategically add color to the form.
Oftentimes an assistant will gather a small bit of clear glass from a batch in the glory hole. The assistant will approach the gaffer, who is usually seated and constantly turning the parison, who will stop turning the piece while the assistant attaches the punty with the molten glass at the opposite end.
The gaffer then taps the blowpipe and it breaks away, leaving the parison attached to the punty. If the glass is dropped during this process, as often happens with novices, the piece has to be recreated from scratch. There is no salvage.
Opening the Parison
The gaffer takes the punty and once again returns it to the heat of the glory hole. Afterward, a variety of tools are used to gently create the mouth of the vase or bowl that is being created. Once the gaffer is satisfied it is time to cool the piece.
Using the Annealing Furnace to Cool
As discussed in “tools and terms” earlier, the annealing furnace or lehr is used for controlled cooling of the glass piece to keep it from cracking while it returns to its solid form. The temperature in the lehr does not exceed 516° C and from there the piece is cooled very slowly and gently over a period of 14 hours until the glass finally reaches room temperature. After this point the glass is taken to the “cold shop” to be polished and have the final decorative details added if necessary.
If you’re considering learning how to blow glass, remember that it takes time, dexterity, and a lot of patience -- especially when learning -- to master this ancient craft.