Kiln Induction and First Kiln Loading and Firing

Today’s induction was hosted by Matt the Ceramics TD, who showed the group how to arrange shelves and ceramics work in the kiln for a bisque firing. We then got to load up a bisque kiln partially under his direction.

The kiln room boasts several large electric kilns which are of varying ages, and a few large gas kilns, all front loaders, a few electric top loaders are available too with a couple specifically for glass and enamelling. I intend to use the glass kilns for large enamel pieces in the near future. The shelves are stacked in the kiln using 3 kiln props for each shelf, 2 at the back one at the front – 3 points of contact are more stable or at least easier to get stable than four points. The first shelf goes on props not the base of the kiln. There are specific shelves for specific kilns (such as size, thickness), also check that shelves are not bent, they sag over time and use. Load shelf then props then work then next shelf etc. Smaller work should be placed at the bottom of the kiln with bigger work at the top –  this is thought to be a more stable arrangement and lets bigger pieces fire better and to ‘soak’ in the hotter top of the kiln. Remember to leave gaps between glazed work of at least 1cm. Use the powdery side of the shelf face up for the work to sit on – this stops glaze run-off sticking and cracking shelf.

The main risk in using kilns are overfiring and, if careless, burns to skin or face. The kiln must be turned off at the right time so carefully preparation and monitoring is essential. Bisque firing  vent closes at 600C and glaze firing closes at 300C. The spyhole bung must remain in at all times when not observing pyrometric cones. The kiln casing can also get super hot so watch out when working around them.

Pyrometric Cones

  • Used for measuring heat and glaze behaviour mark point.
  • The cone is positioned to the left of the spy-hole in a small blob of clinker clay leaning on its base, it is positioned as stated so that when it bend in the heat it is still visible. When the cone reaches the shelf surface the kiln has hit its required temperature and should be turned off. (If spyhole is hazy with gases when viewing cones then open the top vent for a few seconds to clear it then cover up top vent again.
  • Only open the kiln once it has cooled below 150C.

Kiln Regulator

  • Start on 20-50% to get up to temperature.
  • Don’t set the temperature regulator to 100% straight away!

Matt’s Firing Guidelines

  • Start the kiln on 10% for 1 hour.
  • Next hour turn to 30%.
  • Probably about 300C by this point – close top vent on the kiln (600C if bisque).
  • Then 50% for an hour.
  • Then 75% for an hour.
  • Then 100% to cone up to cone bending.
  • When the pyrometric cone is fully bent turn to regulator to 0% and switch off at plug.
  • Next day when kiln is approx 100C  it will be ok to open.
  • ! When loading kiln be careful not to break the temperature probe at the back of the kiln, its very fragile!
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