All Glossary

Casting Slip

Casting slips are among the easiest clay bodies to make yourself. The ability to make and tune your own will open many doors in your production process.

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Details

To make casting slip you need to understand deflocculation and have a good propeller mixer (with fine-grained speed control, able to run for at least 15 minutes, with enough power and a good propeller). If you are already buying a premixed powder then shifting toward your own recipe will be much easier. Making your own affords flexibility and opens many doors. Commercial stoneware or porcelain casting slips will almost certainly have a recipe similar to that discussed below.

Porcelains and White or Buff Stonewares

Typically, these bodies are 95% clay, silica and feldspar - it is not rocket science. Understanding what each material does enables tuning the recipe to get exactly what you need.

- Kaolin: Most kaolins are non-plastic and so are a natural fit for use in a casting body. White-burning ones are more expensive. Availability and price will likely determine which you use.
- Ball clay: All ball clays are highly plastic, they slow down casting and have less fired whiteness. A few larger particle size ones are available and producers target them to casting. Use one of those. White-burning ones are generally less plastic, thus more likely to be suitable.
- Feldspar: Likely you don't have many available, try the ones you can get.
- Silica: This should be available everywhere and it fires white, use a 200 mesh version.
- Bentonite: At most, only 1% is likely needed (if at all). Get one that is processed to at least 200 mesh.
- Talc: Fine-tune maturity (1-2% additions can markedly increase fired maturity).

L4807 Recipe for Cone 6 (using the most suitable materials in the US)

OptiKast Kaolin 30
Silica 25
KT#1-4 Ball Clay 20
Nepheline Syenite 25
Talc 0.5

As a guide, consider using the slip mixing instructions on the M370 page at PlainsmanClays.com. However, since this uses larger particles clays it will likely require less deflocculant.

Recipe Tuning:
- Increase ball clay at the expense of kaolin for better green strength, better mold release (but slower casting).
- Add bentonite when mold release is poor (it increases drying shrinkage so shrinking piece can pull themselves away from the mold surface).
- Increase Nepheline at the expense of clay for more fired maturity. If feldspar must be used the body will be less mature so more will be needed.
- Glazes should not craze with 25% silica and if the body is mature - if they do then fix them (by lowering their thermal expansion). Glazes may fit with 20% silica, or even 15%, if so then increase feldspar if more maturity is needed, otherwise kaolin.
- Add talc for better maturity (up to 2%, otherwise increase nepheline).

Terra Cotta Casting Bodies: Consider the L4170B (and derivatives) recipe.

Black Cone 6 Casting Stoneware: Consider using a body similar to L4053B, L4768E, L3954F.

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