As I have mentioned in this blog before, it’s not easy being green when you are a ceramic artist, but all around the world, potters and ceramic sculptors are coming up with innovations that are lessening the impact of this artform. It is perhaps even harder to be green when you are a hot glass artist. But after a chance meeting, Fred Herbst, an associate professor in ceramics at Corning Community College, and Steve Gibbs, hot glass programs manager for the Corning Museum of Glass decided to find out it’d be possible to use an anagama kiln to simultaneously fire pots and melt glass for glass blowing. What they came up with was the “Glassagama.”
In today’s post, an excerpt from the March 2010 issue of Ceramics Monthly, which focuses on sustainability in the studio, Herbst explains the design, construction, and results of this hybrid kiln. The Glassagama has the potential to be a ideal tool for small colleges or schools on tight budgets that want to have both glass and ceramics offerings. It’s so cool to see what we can do when we all work together! – Jennifer Harnetty, editor.
There are definite benefits to living and working in Corning, New York. Corning, consistently rated as one of the top small towns for art in the US, is home to the multinational glass and ceramics corporation Corning, Inc., and the internationally renowned Corning Museum of Glass. As an Associate Professor of Art at Corning Community College (CCC), I have benefited immeasurably from the intellectual, artistic, and material resources found in this community.
A direct connection with the Corning Museum of Glass came in 2006 when I met Steve Gibbs, the museum’s hot glass programs manager. This chance meeting has proven to be an important moment for me in the development of my work with wood-fired kilns, ceramics, and glass. Gibbs had an existing interest in the construction of a wood-fired glass furnace as a demonstration tool of ancient glass technology for the museum. I invited him to attend the next firing of the CCC wood-fired anagama kiln and then work with us on future firings.
Glass Blowing Terms
Anneal: the process of cooling molten glass objects in a controlled manner, finished pieces are placed inside a heated annealing chamber to eventually cool at a specific rate over time.
Crucible: a vessel made of very high temperature materials used to hold molten glass.
Cullet: glass chunks that are loaded into crucibles for melting.
Gaffer: a master glass craftsperson, the most experienced glass blower in the team that oversees the production of each piece.
Gather: to collect molten glass from the crucible on the end of a blowpipe or punty rod to be used in the creation of a glass object.
Glass Frit: colored crushed glass that is graded to specific grain sizes.
Punty Rod: also spelled pontil, a solid metal rod that is attached with additional hot glass to the base of a blown glass piece when it is broken from the blowpipe, the punty allows the gaffer to control, reheat, and shape the upper section of the piece.
To learn more about wood firing, be sure to download Wood Kiln Firing Techniques and Tips: Inspiration and Information for Making a Wood-Fired Kiln and Firing with Wood, which is free to Ceramic Arts Daily subscribers!
The first collaborative wood-fired glass and ceramics trial run took place in snowy November 2006 and was highly successful. Over the next few firings, it became evident that the design of our anagama was not ideal for expanding the scope of this research collaboration. We agreed that a new, purpose-built hybrid kiln design was needed. After much discussion with friends and fellow woodfire potters Liz Lurie, Julie Crosby, and Simon Levin, my concept for a new design firmed up. After completing the initial CAD drawings, I worked with Gibbs and Lewis Olson, gaffer at the Corning Museum of Glass to develop the unique glass working elements on this kiln. These features include the large side openings used for gathering molten glass and reheating pieces during the forming process, blowpipe heaters, and a wood-fired annealing chamber.
Gibbs, Olson, and I had a number of specific goals for this new kiln. First, and most importantly, was maximum flexibility in firing and working with ceramics and glass simultaneously. Large side openings would allow easier access for glass blowing and for the development of new hybrid techniques. Next, we were looking for a design that was quicker to load, fire, and cool than the two-week process required with the existing anagama. We also wanted a relatively simple design so that glass and ceramic artists with limited kiln building experience could construct this design and then quickly learn the skills needed to fire. A final critical goal was to make glass blowing as practical as possible “off the grid.” Contemporary glass blowing relies heavily on the use of gas furnaces and equipment to keep the material molten 24 hours a day. This hybrid kiln allows for the use of renewable waste wood fuels in order to fire periodically — saving huge amounts of energy and resources. Construction of the new Corning Wood-Burning Furnace began in November 2007 with a mix of new and recycled refractory materials, and it was fired for the first time in August 2008.
The resulting kiln has an approximate dimension of 12 feet long, 4 feet wide and 5 1/2 feet tall. The chimney is approximately 14 feet high and helps create a very strong flow of flame throughout the chamber. The design dimensions were based on the size of our silicon carbide kiln shelves (18X24 inches) and standard brick sizes in order to minimize cutting. The interior space is approximately 8 feet deep, 4 feet tall, and 27 inches wide. This allows room for three stacks of ceramics, glass melting crucibles, and space for reheating glass.
The physical construction of the kiln started with a layer of cement block on a concrete slab and then three layers of insulated fire brick (IFB) and firebrick forming the floor. The kiln walls are nine inches thick with an inner layer of firebrick and an outer layer of IFB. The kiln roof is made up of two by three foot kiln shelves spanning the walls, next a layer of two inch thick ceramic fiber, and finally a layer of IFB for additional insulation. The chimney flue has a checkered opening pattern that helps create a very even draw throughout the interior. The chimney steps in as it rises to a final outside dimension of 22 1/2 inches square. This part of the structure is tied together with angle steel and threaded rod. The top of the chimney is capped with a spark screen made of expanded metal mesh and steel plate similar to a design we first used on the CCC anagama.
One of the critical elements of this kiln are the large side openings. The sliding doors were designed and constructed from steel and castable refractory by Olson. Garage door wheels attached to the doors run in a special steel channel welded to a support frame that goes over the roof to support all four doors. This feature allows two teams of glass blowers to work simultaneously on both sides of the kiln or for different colors of glass to be loaded on each side of the chamber. These doors also allow a great deal of access to the kiln interior during firing for experiments. Some of the new hybrid techniques that we have worked on include gathering molten glass on a blowpipe and applying it to ceramic pieces and pulling out small porcelain cups to be attached to punty rods so that the piece can be wrapped and decorated with molten glass strings.
Another unique feature of this kiln is the wood-fired annealing chamber designed and constructed by Olson, CCC student Les Lewis, and myself. It has its own independent firebox and flue entrance to the kiln chimney. This firebox has a vertical plate that forces the flame up against a silicon carbide kiln shelf set on edge that forms the front wall of the annealing chamber. The flame is then forced under the chamber floor, which is also made of silicon carbide kiln shelves, to exit in the chimney. The silicon carbide pieces transfer heat to the chamber incredibly well. By maintaining a small fire in the firebox, we can easily hold a temperature between 900 degrees F and 1000 degrees F (480 degrees C and 540 degrees C)in the annealer during the glassblowing time. As each piece is finished, it is placed inside the chamber, and the ceramic-insulation-board door is closed. After the glassblowing has ended, the firebox is closed to burn down and the annealer damper shut. The chamber cools overnight to outside temperature and the glass can usually be unloaded the next day.
Clay and Glass Together
Through our collaboration, we’ve discovered many similarities and new possibilities for hybrid techniques for glass and ceramics. However, there is a major technical difference. That difference is expansion, contraction, and the cooling cycle. If hot glass is cooled too quickly it will shatter or crack. Blown glass pieces must be annealed or slow cooled from approximately 900 degrees to ambient temperature over a span of many hours. In our experiments with applying molten glass to ceramics while in the kiln or loading pieces with glass frit in place, we have discovered that the glass stays attached to the surface. However, it will end up crazed just like normal glaze crazing since the expansion and contraction of the glass and ceramic body do not match.
Loading and Crucible Placement
Each firing is a bit different and has a new set of technical and aesthetic concepts to work with. Over time we have developed a very close partnership and procedure on how the loading and firing will take place. A typical firing begins with the loading taking approximately four to five hours. In this phase, we take our time setting crucibles and ceramic bisqueware bowls to contain the different colors of glass, loading approximately 100 to 150 glazed and unglazed ceramic pieces in specific locations, and working on new techniques such as placing colored glass frits on ceramics. This has become an interesting new option for placing specific colors on pieces and it has opened up a wider palette for wood-fired ceramics.
Once all the work is loaded, the front door is bricked up using a step grate system built into the lower section of the door. This grate design creates channels for preheated air intake and allows precise control of the air moving into the combustion space of the firebox. The beginning of the firing can go quickly with the small chamber, step-grate firebox, and strong pull of the chimney. Even with the danger of going too fast, we have fired greenware in the back of the chamber with no problems. The kiln usually climbs to cone 9 in about 12 hours. The glass in the crucibles will be melted and ready for use at just over 2100 degrees F, but the chamber needs to be closer to 2300 degrees F for effective glass reheating. Once the kiln has reached that temperature, glass blowing normally begins and can continue as long as needed. While the glass blowers are working together as a team to create each piece, another team will be keeping careful watch on the firebox in an attempt to maintain the temperature at an appropriate level. However, we often experience a slight drop in temperature after an extended period of glass blowing. Fortunately, the kiln is very responsive and will climb back up after a short pause in glass work and some aggressive stoking.
We’ve found that the design of the Corning Wood-burning Furnace has a number of advantages. Based at CCC in partnership with the Corning Museum of Glass, the kiln serves an educational, demonstration, and research role. Participants in the firings get hands on experience with both the basics of glass blowing and wood-fired ceramics. This design has proven itself ideal for college and university programs or for craft centers looking to expand opportunities for students. The smaller size, faster firing and cooling cycle also gives us a quick turn around on new ideas. In addition, working together, ceramic and glass artists use resources in a more efficient and sustainable way. When the annealer is firing, the combined heat of both chambers burns nearly all of the smoke off in the chimney base, creating very clean emissions. Our fuel is a mix of species coming mostly from local tree services and the state department of natural resources looking to get rid of diseased or damaged trees. The large firebox and stoke door helps to minimize the amount of wood splitting required. For most wood-fire artists, that is one of the most important advantages.
There are a few disadvantages with this kiln as with any design. The small chamber size can be difficult to load, requiring some contorted positions and joint strain to place kiln shelves. The firebox is very powerful and produces a relatively quick stoking cycle. If the crew isn’t paying close enough attention, the temperature can drop quickly. Fortunately, that same power allows for a quick recovery, ensuring adequate temperature for a successful firing.
Spreading the Word
The summer of 2009 brought about a new era for the Corning Wood-Burning Furnace. On June 11th, hundreds of people attended a firing and glass blowing demonstration as part of the Glass Art Society international conference. Gibbs narrated as Venetian master glass blowers Davide Salvatore and Elio Quarisa demonstrated their amazing techniques to a captivated crowd. The next step took place in September 2009 at the Domaine de Boisbuchet (boisbuchet.org), an art, architecture, and design international educational center in Southwestern France. Working with Gibbs and Jean-Charles Prolongeau, ceramics professor at ENSA Limoges in France, I constructed and fired version two of our hybrid kiln. Now nicknamed the “Glassagama,” this design proves that cutting-edge research and 16th century technology are not mutually exclusive.