Creating Slumped Bottles With a Large Ceramic Kiln - A How to G

  • Typically a smaller glass kiln is used in the process of slumping or melting glass. The larger kilns are designed for the purpose of firing ceramic pots. Glass slumps at about 1425 degrees Fahrenheit. When glass reaches this temperature you are supposed to open the kiln door and crash cool the kiln down to 1100 degrees Fahrenheit. This is called crashing the kiln. Crashing the kiln prevents your slumped cool water bottles from coming out looking like there is a haze on the surface instead of being clear. When this happens your glass has devitrification. After you crash cool your kiln, turn it completely off and let it cool naturally until the next day.

    There are tricks to using a larger kiln. When working with a larger kiln to slump glass you need to check the various levels of your kiln by checking the side peep holes to look in to see how the insulated water bottles are doing. You may need to go slightly beyond the 1425 degree mark if not all of your bottles have slumped. You need to keep a close eye on your kiln at this point.

    A common ceramic kiln has three separate layers. You could use just one or two layers to melt the bottles. This would give a more unified overall temperature and produce fewer variations in the bottles; but I always use all three layers of my kiln. Sometimes the bottom layer might not totally slump. It is said that heat rises and that holds true in my kiln as well. The top layer is usually perfectly slumped while the metal water bottles in the bottom of the kiln may slump but not to the point where the bottleneck opening would close down on a wire hanger. Using this technique you can create both wired slumped bottles (which make beautiful wall hangings,) and unwired pieces that can become serving trays or other items.

    Keep a firing schedule of time and temperature. Also keep notes on what is happening in the kiln on the various levels. I recommend you also take notes when emptying your kiln after the firing and note the location of various colored stainless steel vacuum bottles and how they slumped at the different levels. You will find that clear glass bottles will usually slump well on the bottom level of your kiln where blue and green might not do as well. Of course all kilns are different and you certainly need a pyrometer, which measures the temperature of your kiln. If your kiln has an automatic cone shut-off feature, you'll want to use a higher level cone so it will not shut your kiln down while firing your load of bottles. I recommend using an 05 or 06 temperature cone. An 013 cone melts at 1485 degrees F. Any cone that melts at a higher temperature will do the trick.