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Glass: The beauty of art and the mystery of science.
A clue in the molecular mystery of liquid glass
by Bethany Hubbard
April 22, 2011
Bethany Hubbard/MEDILL
Artists at Chicago Hot Glass work with the molten medium that is heated to more than 2,000 degrees.
Bethany Hubbard/MEDILL
Recent research has uncovered the molecular motion of glass-forming liquids.
The molecular makeup of glass has puzzled scientists, and challenged artists for centuries. At more than 2,000 degrees, glass is as volatile in its liquid form as it is when cool.
“Our furnace here is a heated chamber that’s heated to about 2,100 degrees,” said Danny Ellis, a studio technician with Chicago Hot Glass in Humboldt Park. “It has basically a big pot in it that holds about 300 pounds of melted glass when it’s full.”
The flexibility of glass makes it a desirable art medium. Yet the process of crafting it requires patience and intuition.
First an artist takes a long metal, hollow pipe and dips it in the hot glass in the customized, super-hot furnaces.
“At that temperature the glass has a consistency about of honey, so you’ve got to keep spinning it, otherwise it’s going to drip right off,” Ellis said.
As the molten glass is collected on the end of the pipe, artists can shape it, or let it cool and, as it stiffens, add more glass or color, according to Ellis.
“You can tell how hot your glass piece is by how it’s moving,” said studio technician Kit Paulson. “So if you find that you’re turning the pipe very quickly to keep it on center, that’s a hint that it’s very, very, very hot. And if it’s not very difficult at all to keep it on center that means that it is comparatively cold, like 2,000 degrees rather than 2,150.”
Teamwork is essential in the glass blowing process. Artists help one another by blowing in the pipe to inject air into the glass to expand it and hollow it out for pieces such as a bowl. Final shaping is done with wooden blocks and wet newspaper.
Mid-process, pieces are transferred to an iron rod called a punty, on which the artist can make finishing touches. When a piece is complete, it is gently separated from the punty and placed in the annealer, a temperature-controlled oven where the completed pieces are slowly cooled down.
Scientists have struggled for centuries to understand what happens to glass on a molecular level as it changes temperature. Though glass making traces back to Egyptian times, much of the art form relies on intuition rather than science.
“If you want to understand it on that level, there’s quite a bit to know, but you can as an artist simply approach it as a liquid medium,” said Daniel Staples, president of Chicago Hot Glass.
While artists rely on intuition in order to understand how glass acts, scientists continue to theorize about its molecular makeup. What happens when glass transitions from its fluid form to the hard yet fragile material that plays an essential role in our daily lives? This question has puzzled scientists and manufacturers for centuries.
“Not surprisingly, the glass transition is currently regarded by many as the deepest unsolved problem in solid state theory,” wrote Karl F. Freed, of the University of Chicago, in “The Descent into Glass Formation in Polymer Fluids.”
So much of our world depends on glass - from windows in buildings and cars, to the glasses we drink from and the ones that correct our vision. Understanding how temperature affects the molecules in glass means more efficient production of the items we rely on.
Jack Douglas is a material scientist in the Polymers Division of the National Institute of Standards and Technology in Gaithersburg, Md. In their recent Physical Review Letter, Douglas and his colleague Francis Starr of Wesleyan University reported on basic insights they have gained about the molecular motions of glass-forming liquids.
“One of the most important things about the everyday phenomenon of glass formation is the relatively slow rate of flow, or the gooeyness or viscosity of these complex liquids before they freeze into solid glasses,” he said, adding that consistency plays a huge role in the making of glass materials.
“Many foods, including candies, biological materials broadly, and structural materials ranging from plastics to window glasses" heat and cool in a similar molecular manner. "So we are talking about a very basic materials science problem, “ he said.
Douglas and Starr’s most recent research suggests that as the material cools and increases in viscosity, the molecules form strands that grow and lengthen.
“They are like little snakes, and they’re growing and getting longer and longer,” he said. “There is a direct correlation between how long they are and the gooeyness.”
Douglas likened this string-like motion to the movement of people in crowds who are all trying to get on the subway at rush hour. Someone stumbles or lurches and a chain of movement runs though the crowd, he said.
“The only way for the molecules in viscous glass-forming to go from one place to another is to migrate in snake-like molecular flocks,” he said. “Knowledge of this phenomenon should allow for the design of diverse new materials by stabilizing nanostructures in advanced manufacturing applications.”
Douglas said that this information should be useful in the enhanced preservation of foods and protein drugs, and said that he and his coworkers are actively investigating how ordering processes in other materials may mimic the molecular motion of glass-forming liquids.
For artists, such a discovery won’t change the way they work. Part of the craft is embracing the challenge.
After 10 years as a glass artist, Paulson said that she still finds the craft hard, which is something she likes about it.
Ellis said that an understanding of the material can only be achieved through doing.
“There are a lot of little steps, little nuances, like your balance in handling the molten glass to keep it centered, and trying to get the colors and the patterns to do certain things. You can only experience those, they’re hard to explain.”
