Each type of clay and organic plasticizer offers different degrees and types of plasticity with a different set of advantages and disadvantages. The nature of plasticity and subtle differences between combinations of plastic materials is a complex subject and understanding it better can open new doors of efficiency, quality and cost reduction.
•The secret to cool bodies and glazes is a lot of testing.
•The secret to know what to test is material and chemistry knowledge.
•The secret to learning from testing is documentation.
•The place to test, do the chemistry and document is an account at https://insight-live.com
•The place to get the knowledge is https://digitalfire.com
- Ball clay is the main plastic material used in clay bodies of all types. It is much more plastic than kaolin but also has much higher dry shrinkage and higher iron content. A typical white high temperature stoneware is often about 25% each of kaolin, ball clay, feldspar and silica.
- Moderately high percentages of the Alkatrol products can be substituted in body compositions to reduce laminations in pressing and to aid in extrusion.
- 1 part bentonite can plasticize a body as much as 10 parts kaolin. Bentonitic bodies are stronger in the dry form but dry slower, crack more and fire darker with potential iron specks (get a super fine ground grade).
- It is possible to make a plastic throwing body using 50% kaolin only, however you must choose one of the highly plastic varieties such as #6 Tile. Even then you will likely need a little bentonite to augment the kaolin. There is a huge range in kaolin plasticities, test for yourself to find out.