Fire polishing glass is a method that glass workers use to garner a smooth and glossy appearance on their works. People who grind their fused (melted portions of glass) pieces use this technique to achieve a uniform, shiny appearance around the edges. Polishing is also used by artists who do lampworking, which is the procedure of shaping glass at a table-mounted torch, to ensure a clean appearance of the work. In each instance, extremely high temperatures, between 1,300 degrees and 2,800 degrees Fahrenheit, burn away impurities and allow the glass to maintain a crystal-clear display.
Before polishing glass, acquire the necessary tools to set up a studio, which include a kiln and ventilation system (fusing and lampworking), and/or a torch kit (lampworking). To begin, purchase a kiln, an oven that retains high heat and gradually brings down the temperature, to anneal (remove stresses) in the glass. Find an appropriate kiln for your purposes (fusing or lampworking) and buy from a ceramics or lampworking supplier. You can often find process-specific kilns on the Internet using search terms like "fusing kiln" and "lampworking kiln" or attend a trade show to see these tools up close and ask the vendors questions.
Furthermore, fusers also will need either kiln wash or fiber paper to protect their work in the kiln during the polishing process. These materials are also available from a ceramic or glass supplier.
Next, place a ventilation system in your studio to protect against dangerous vapors. You can use a big box fan in a window or opt to set up a vented hood system above the torch or kiln.
Lastly, lampworkers must have a torch kit (available from a glass supply vendor), which consists of a table-top torch, oxygen and propane hoses, basic tools and a sampling of glass. Additionally, didymium lenses are also included because glass workers must wear these glasses to protect the eyes against sodium flare. Outside of the kit, lampworkers need a propane and oxygen supply to power the torch. Propane tanks (like those used for barbecue grills) are available from gas stations and pressurized oxygen tanks are found at welding shops.
In general, it can cost between $200 to more than $5,000 to set up a workspace for making glass. This all depends on the types of tools that you purchase–especially the kiln.
Using a Kiln
Depending on the type of glass (for example, Bullseye or Spectrum), fusers use a range of temperatures and heating times to attain the desirable look.
Begin by placing the glass inside the annealer on top of the previously installed fiber paper or kiln wash. Read the specific instructions on the package to add it to your kiln properly.
Next, check with the manufacturer of your glass to see what the recommended polishing schedule is. You can often find this information in the company's literature, or access its website for a detailed report. If you do not have this data, use 1,300 degrees as the polishing temperature and maintain this high heat no longer than 20 minutes so that you do not inadvertently distort the glass. A general polish procedure is to heat the kiln at a rate of 400 degrees per hour until it reaches 1,000 degrees, and then hold it there for 20 minutes. Now, as quickly as possible, raise the temperature to 1,300 degrees, holding for five minutes. Quickly lower the temperature down to 950 degrees and hold this for 60 minutes. Finish by dropping the rate down 400 degrees per hour until it reaches 100 degrees, and then turn the kiln off. Most kilns come with a controller that allow you to program the temperature setting, with the exception of quickly cooling the temperature; whereby, you open the kiln door to rapidly lower the degree rating.
During the process, keep a detailed log of the temperature and times you use that achieve the best effects so that you can repeat these results again. Additionally, polishing techniques may differ from person to person, depending on the type of glass and kiln used.
Using a Torch
Lampworkers have the benefit of fire polishing their work quicker and of seeing the process take place. Oftentimes, this technique is used to remove a cloudy appearance on the work, or when the glass artist wants to melt in the mark left over from detaching the holding rod (punty) from a piece of glass.
Start by inspecting your piece during each phase of creation or during the completion of a project. When glass is cooler than ideal and the flame splashes against it, a hazy coloring forms on the surface. To rectify this, simply rotate the affected portion in the heat of the flame and watch as the haze dissipates. You may also hold your glass piece up to a light to view the reflection off of the glass.
When removing a punty, whether melting it off in the flame or cracking it off, a mark (scar) is always left over, which could be sharp. To protect the appearance and safety of your work, hold the glass against the side of the flame and watch the protruding scar recede back into the body of the glass. This process normally takes no longer than a few seconds.