Pottery and Ceramic Firing Chart

Fact 1:  To become HARD AND GLASS-LIKE, clay must be fired. This means that it must be baked in a special furnace, called a kiln to a minimum temperature of about 1112° F. 

Ceramic glazes each have a temperature range that they should be fired to. If the glazes are fired at too low a temperature, the glaze will not mature. If the temperature goes too high, the glaze will become too melted and run off the surface of the pottery. For success, a potter must know their glazes’ temperature ranges at which they become mature.

When potters talk about ceramic firing ranges, they are usually referring to the three most common: low-fire, mid-range, and high-fire ranges. In regards to glazes, we need to add two other ranges: very low-fire, and lower mid-range firing ranges.

A kiln temperature can be measured in three ways:

  1. KILN PEEPHOLE
    • The color of the kiln atmosphere. 
      We look through the peepholes in the wall of the kiln and simply note the color inside.
      The atmosphere in the kiln glows red at about 932° F, then turns orange to yellow to white as it gets hotter. 
      By 2372° F the atmosphere is white hot and damaging to the naked eye.
  2. PYROMETER
    • This is a thermometer capable of registering high temperatures.
  3. CONES
    • Cones are the most accurate method because they measure the effects temperature has on the clay over time, the working temperature.
      Often clays and glazes are referred to by the Cone number to which they are best fired, such as, a Cone 9 glaze or a Cone 8 porcelain, and so forth. 
      The Cones themselves are small pieces of specially formulated clay which begin to melt at specific temperatures. 
      They are placed inside the kiln so that they can be seen when one looks through the peepholes while the kiln is being fired. 
      When the Cone begins to melt and bend over we know that the specific temperature has been reached. 

WHAT HAPPENS AS CLAYS AND GLAZES ARE FIRED

212° F

  • Water boils.

212 to 392° F

  • Clays loses water.

392° F

  • Typical kitchen oven baking temperature.

705° F

  • Chemically combined water leaves clay.

932° F

  • Red glow in kiln.

1063° F

  • Quartz inversion

….. SLOW, CAREFUL FIRING UNTIL

1112° F

  • cone 022 (approx. 1112⁰F – 605⁰C)

1472° F

Cone 015 

  • Organic matter in clay burns out.

1472 to 1832° F

  • Orange color in kiln. 
  • Low fire earthenwares and lowfire lead glazes mature. 
  • Normal firing temperature for red bricks and terra cotta pots.

Cone 015 to Cone 07 

Cone 013 (approx. 1566⁰F – 850⁰C)

Cone 012 (approx. 1623⁰F – 882⁰C)

Cone 02 (approx. 2048⁰F – 1120⁰C)

This range is usually used for luster glazes and very low-firing overglazes. Ware must be fired at least once at a higher temperature first, in order for the clay body to mature. The ware will often not only go through a bisque firing, but also a higher temperature glaze firing. Very low-fired overglazes and lusters are then applied to the already fired primary glaze. The ware is returned to the kiln for a very low temperature firing in order to fuse the overglazes.

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04 of 05 Mid-Range from cone 4 (approx. 2167⁰F – 1165⁰C) to cone 7 (approx. 2264⁰F – 1210⁰C)

This range is being used more and more as potters become more concerned about energy and fuel usage. Another factor has been the availability of electric kilns that can comfortably reach this range without severely decreasing the kiln’s and the kiln elements’ lifespans. Other advantages to firing in the mid-range include ability to adjust and use stoneware clay bodies to this range in turn, mid-range stoneware bodies increase the durability of the ware mid-range glazes are also more durable than those fired at lower temperatures, and there is still a fairly extensive color range available.

1832 to 2120° F

Cone 07 to 1 

  • Yellow color in kiln. 
  • High fire earthenwares mature. 
  • Feldspars begin to melt.

2138 to 2174° F

Cone 3 to 4 

  • Bright yellow white color in kiln. 
  • Mid-range clays and low fire stonewares mature. 
  • High iron content clays begin to melt.

2282 to 2345° F

Cone 7 to 9 

  • from cone 8 (approx. 2305⁰F – 1260⁰C)

White color in kiln. 
Stoneware clays vitrify, feldspathic glazes mature.

2345 to 2462° F

Cone 9 to 13 
High fire stonewares, porcelains vitrify.

  • cone 14 (approx. 2530⁰F – 1390⁰C)

This range includes the stonewares and porcelains. Glazes and clay bodies are dense and durable; however, the color range is limited. Because of the varying effects of oxidation and reduction on glaze colorants, the few coloring oxides that are viable at this range can still produce a rich, if much more limited, palette.

MOST STUDIO POTTERY IS FIRED TO CONE 9 OR LOWER.

3113°

Silica melts

3722°

Alumina melts