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  • Burner Port - the hole that the burner faces and where the flame enters the kiln
  • Flue - the hole where the combustion gases leave the kiln
  • Bag Wall a wall inside the kiln that protects the ware from direct flame from the burners, usually just inside from the burner ports in downdraft kilns
  • Chimney - a tall hollow shaft that carries kiln gases up away from the kiln. Its height helps create a draft in the kiln pulling secondary air into the kiln. It also can increase the amount of primary air by creating a negative pressure difference at the burner ports.
  • Damper - a piece of refractory or steel to close off the damper
  • Passive Damper - a hole in the chimney that can be opened or closed to reduce the effectiveness of the chimney. Passive dampers can also reduce pollution by adding oxygen to hot kiln gases allowing them to burn more as they exit the kiln
  • Spy Hole aka Bung , a hole allowing you to look into the kiln at cones. A soda or salt port is essentially the same thing but with placed to allow introduction of fuming agents
  • Oxidation - firing with more oxygen then is needed for combustion. In electric kilns since there is only combustion of trace organic matter in clay, this is the normal state.
  • Reduction - firing without enough oxygen to completely burn the fuel. This creates carbon monoxide CO), and can create hydrogen (H2). The CO or H2 combines with oxygen from iron oxides and copper oxide and changes the color of clay and glazes.
  • Neutral - A state where a kiln has neither oxidation or reduction. It should be considered unachievable
  • Back Pressure - When gases are blown into the kiln, and when they combust they increase the pressure in the kiln. Backpressure happens when there is more pressure in the kiln than outside it. It varies top to bottom. There is almost always backpressure at spy holes high in the kiln. For our purposes at TAMUCC sufficient back pressure in order to prevent leaks from the door or floor from creating a zone of oxidation in the bottom of the kiln is when there is a very small amount of back pressure at the bottom spy hole.
  • CH4 + 2O2 -> CO2+ 2 H2O
  • Methane plus oxygen yields carbon dioxide and water
  • Carbon Monoxide - This is the most common reducing gas in kilns. It is poisonous and flammable. In sufficient quantity it is also explosive.
  • Soot - If you reduce a kiln hard, or if the burners do not mix gas and air well carbon, soot, can be created. Much of it can leave the kiln unburnt. It can also be trapped in glazes, an effect called carbon trapping. Carbon trapping mostly happens at around cone 010 in shino type glazes. It can also be trapped when soda or potash is introduced into soda kilns.
  • Carbon Trapping
  • Kiln Shelf
  • Kiln Post
  • Cone Pack - A group of cones in clay used to measure temperature
  • Body Reduction Reduction of the clay body before melting of the glaze and before the clay starts to vitrify.
  • Glaze Reduction - reduction near the end of a firing.
  • Reduction Cooling - reducing a kiln while it cools.
  • Quartz Inversion - Quartz, a structural arrangement of silica has two forms alpha and beta. The arrangement of the atomic bonds is the same in both forms. The angles of those bonds change. The change on heating ( or its inverse on cooling) from alpha to beta forms happens at 573 °C (1063˚F). This change is accompanied by a linear expansion of 0.45% (this is a 1.3% expansion volumetrically)
  • Cristobalite Inversion - Cristoballite is a different polymorph of silica. This means its atoms are arranged differently than quartz. The atoms are bonded in a different pattern. It too has an alpha and beta form that go through their inversion at roughly 250˚C (482˚F) according to much literature. Tests on clay show it happening around 200˚C (392˚F). Cristobalite is sometimes introduced into clay bodies with grog made from firebrick. At higher temperatures (I cannot find definitive numbers for this) silica is expelled from the kaolin molecule. This fine silica, if not dissolved into a glass, is expressed as cristobalite. Quartz converts to cristobalite over time starting first on the surface of crystals. The longer the time at elevated temperatures the more quartz converts to cristobalite. Feldspar is often included in stoneware bodies to promote a glass phase that dissolves much of the cristobalite.
  • Bisque Firing
  • Glost or Glaze firing
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Page last modified on March 07, 2019, at 11:08 AM