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Notes on Kiln Firing.

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Notes on Kiln Firing.
by Peter Stephens. 2006.


 

 

 

 

 

 

 

 

Notes on Kiln Firing is a practical guide to the elements and factors involved in firing a kiln for the first time. Some of the FAQs of students during the year of a pottery class.  

 

 

 

 

 

 

 

 

 

 

 

 

Page Index

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 Introduction


    FAQs

  1. When can I fire my pots?

  2. What temperature do I fire to?

  3. What is a bisque?

  4. What is a Glost or Glaze firing?

  5. Do I need to bisque?

  6. What glaze can I use?

  7. What cone do I need?

  8. What kiln can I use?

  9. On an electric kiln,
    what temperature controller settings do I use?

  10. In an electric kiln when do I plug the holes?


     FAQs

  1. What is the rate of rise?

  2. What are the critical points in the
    development of the ceramic body?

  3. What is reduction?

  4. Why is it so difficult to light the gas burners?

  5. Why is it important to be oxidising, not reducing under 1000°C?

  6. When is a firing complete?

  7. What is a soak?

  8. Why did my pot crack?

  9. Why did a piece fall off?


 

 

 

Diagram Index

    Diagrams

  1. Using a kiln sitter

  2. The parts of a kiln and a gas burner.

  3. Adjusting the rate of temperature rise.

  4. Critical points in firing.

  5. Which kiln firing?

  6. Firing chart (template)

 Documents

 

 


Written, drawn, designed, and produced 2006 - Peter Stephens
Free for distribution.



 

Notes on Kiln Firing.

Introduction.

A pottery firing changes the plastic clay body irreversibly into a hard ceramic body. Bisque fires to about 950-1000° C . It still has some porosity and so will absorb water. Over 1000° C the body will start to become vitrified, glassy, and impervious to water. Usually for ease of handling the pottery there are two firings, first the bisque, also called biscuit, and then after the pots have been glazed, the glost or glaze firing. To change the plastic clay pots, greenware, into a bisque, heat is applied by electricity or by burning a fuel such as gas. The rate of temperature rise is modified by the ability of the clay to withstand the increase of temperature. And also by the need for the clay to be properly developed at the molecular level to provide structural strength, resistance to wear, and hygienic use. To achieve this you need to be aware of the progress of the firing, taking in to account the following;

  1. How much pottery, volume of material, is in the kiln. That is, the density of the packing.

  2. What is the condition of the kiln and its capacity to reach a high temperature in good time.

  3. The amount of available time. There may be time limits to the use of the kiln.

  4. Your timetable.

Generally the firing procedure is straight forward. Increase the fuel via the burner, or turn up the electric controllers. The overall purpose is to give the clay and glaze a strong, beautiful finish. A fast rate of increase, a quick firing, is possible, but this leads to many problems, such as cracking of the ware, glaze imperfections, and poor body strength which shortens the life of the ceramic. So we need to consider the reasons for adjusting the various controls and why a controlled temperature rise is necessary. Think of a lump of clay. The heat has to penetrate deep within the lump evenly through to the center. During this time the changes to the clay have been taking place gradually from the outside in. The release of water and other combustion gases, the burning out of carbonaceous matter, is not complete unless the heat is given time to penetrate the clay. At the same time the heat is making molecular changes to the clay. Too much heat too fast and surface molecular changes will take place before any expulsions have had time to get out, becoming trapped inside. Such an uneven and impure body is structurally weak. The major points of transition are;