The science behind glassblowing
By: Marisa Sloan
What do the Hubble telescope, the windows of Notre Dame, and your favorite bottle of wine have in common? They’re all made with glass.
Trying to imagine a world without glass is almost impossible. For many people, the glass screens of their phones are the first thing they see in the morning, and their glass light bulbs being turned off are the last thing they see at night. All this is possible thanks to the contributions of glassblowers over 2,000 years ago, and a glassblowing process that has remained nearly the same for just as long.
The Olio, which opened in 2014 in Winston-Salem, is an educational glassblowing facility featuring a youth apprentice program and retail gallery. To learn more about the science behind blowing glass, founding executive director Rebeccah Byer and creative director Sarah Band offered to take a moment away from the furnace to talk about their own experiences with the art.
“It’s a really great way to show science in practice because we can take the concepts that students are learning in their books and apply them in real action,” Byer said. “We’ve had elementary school groups come in for their heat induction section; we’ve had high schools come for chemistry; we’ve had [a class on] the history of alchemy from Wake Forest University; we’ve had a lot of different groups come for a lot of different focuses.”
Glassblowing is exactly what it sounds like: a glass-forming technique that involves blowing molten glass into a bubble to shape it. A glassblower will begin at the furnace, which houses a large crucible of molten glass. They then use a long, hollow tube called a blowpipe to gather molten glass the same way a honey dipper is used to pick up honey (although it probably isn’t as delicious).
The molten glass is rolled on a “marver,” a flat piece of steel, in order to slightly cool and shape the outside of the glass. Next, the glassblower creates a bubble by blowing into the blowpipe. Once it reaches the desired size, an iron rod called a “punty” is attached to the opposite, bottom end of the molten glass blob so that it can be shaped with shears, tweezers, wooden paddles and water-soaked newspaper.
Because the molten glass must remain above a certain temperature while being worked on, a secondary furnace called a “glory hole” is used to periodically reheat it during the shaping process. Then once the piece is complete, it is put into a third and final furnace called an “annealer.” The annealer slowly cools the glass to room temperature over a period of days, depending on the thickness and size of the glass, to prevent cracks from thermal stress.
While it’s true that some of the techniques and tools are more refined today, the tried-and-true process has remained almost the same since the inception of glassblowing.
Today, most glassblowing studios order glass from glass manufacturers and reshape it to fit their needs, rather than making the glass themselves. This is because it can be a difficult process. The type of glass used in glassblowing is created from sand (silica), soda (sodium carbonate) to lower the melting point, and lime (calcium carbonate) to increase the durability of the glass. The transformation of these raw materials into glass requires a furnace at about 2,400 °F, while most glassblowing requires only 1,350 – 1,900 °F to melt down the glass and keep it pliable for working.
Silica, the major component of glass, is a mineral found only on special beaches with high percentages of silica in their sand. When lightning strikes this sand, over 100 million volts melt the silica together and form a hollow, branching tube called a “fulgurite.”
And — spoiler alert — despite Josh Lucas’ character in Sweet Home Alabama making a living off of sculpting fulgurites into beautiful pieces of glass art, it’s actually a relatively rare phenomenon.
In fact, Byer said there’s a shortage of silica, and glassblowers are feeling the effects. Now the second most used natural resource behind water, thanks to it being a primary component in building materials like concrete and glass, silica is running out.
“The earth doesn’t have an unlimited supply of high silica content beaches or high silica sand,” said Byer, emphasizing the role that climate change and rising sea levels are playing in the loss of beaches.
That’s why sustainability has remained at the forefront of The Olio’s mission. All of the glass used at The Olio is made from almost 100% recycled waste glass that is donated by the local community. After five years of sustainability, it’s recently become an even more important practice following the City of Greensboro’s abandonment of almost all glass recycling.
“What we contribute to the landfill is significantly less than any other glass studio,” Byer said. “What we divert away from the landfill, from collecting from the community over time and also collectively nationwide, this system could do a serious service to our landfills and to our recycling systems.”
Despite this, The Olio is only one of few glassblowing studios in the country that uses entirely recycled glass. That’s because there are as many different types of glasses as there are metals, and although “olio” means a miscellaneous collection of things, “if you mix different types of glass together and you don’t know where they come from or how they were made, everything can crack and explode,” Byer said.
Different types of glass are categorized by their coefficients of expansion (COE). Glass expands when it is heated and contracts when it’s cooled, and the COE describes how much a glass will expand for each degree of temperature that it is increased. That’s why when glasses of different COEs are mixed together, despite perhaps looking the same to the naked eye, there’s always the risk that one will cool faster than the other and the whole thing will explode.
“If you look in your pantry at home, for example, and you look at all the different jars that maybe your pasta sauce comes in, each of those jars has a different coefficient of expansion,” Byer said. “The COE that we use in our studio is 96.”
Standard window glass has a COE around 84-87. Glass that has boron added to it, such as glass used in bakeware like Pyrex, has an exceptionally low COE of 33 so that it remains intact despite the high heat of an oven.
Glassblowing studios that recycle glass have to be careful about where they’re getting their glass from and how they keep it sorted, in order to avoid melting different types of glass together. The Olio, however, avoids this problem by using a patented formula that transforms any type of glass into 96 COE. The formula was developed by Christian Thornton, a glass artist based in Oaxaca, Mexico, and Byer and Band have been successfully using it at The Olio for five years without a problem.
“We’re able to take all the different jars, mix them together — liquor bottles, wine bottles — and we add this formula and it makes them all one cohesive glass,” Byer said.
The Olio is only one of two glassblowing studios in the country to use the formula, but Byer and Band have hopes to change that.
“We can now go into other studios and help them figure out a system that would work for them to not be too costly on their time, or manpower, or space limitations,” Byer said. “I feel that we can really adapt this system to any other studio that wants to use it. It can be done in any capacity.”
The same way that different combinations of materials in glass can cause it to have a different COE, the addition of different metal oxides to glass can cause it to change color as well.
A lot of toxic, heavy metals are currently used to create color, although some glassblowers are trying to find alternatives to these. Cobalt oxide is used to make blue, lead oxide is used for yellow, iron for greens and blues, uranium oxide for fluorescent green, and sulfur oxide for amber. The list goes on and on. Gold and silver are also used, with red and pink colors being almost exclusively achieved using gold, but are expensive and therefore more rare in studios.
Depending on which metal is being used, each metal ion has a different number and shape of electrons surrounding its nucleus. Color is created when the metal ions absorb certain wavelengths of light, and which wavelengths are absorbed depends on how the different shapes of electrons interact with other molecules in the glass.
“What we do is really rooted in the science of glassblowing, and the science of art, and how to ignite and inspire people,” Byer said. “When [kids] come into our studio and they see science in action, they go back to school and they’re a little bit more interested in the chemistry or the physics lab. It’s a way for people to make those connections.”
If you’d like to learn more about The Olio or glassblowing, visit The Olio’s website.