The Role of Deflocculants in Ceramic Works

Clay is a simple and handy material that is used for various purposes. Potters use it on their wheel and so do industries to make bricks and tiles. Lovely earthenware and porcelain products can be fashioned from the plain clay powders. The decorative options are almost limitless.

Clay is easy to use as well. The fine soil is mixed with water to form a liquid clay slip. This mixture can be used on the potter’s wheel or poured into plaster molds to create the desired shape and form. The plaster absorbs the water in the clay slip thus allowing the clay to harden and shrink as it cures. Once cured, the mold is broken away to reveal the charming clay figure inside.

At times, things can get a bit complicated here. For instance, the clay may settle at the bottom of the mold leaving the watery mixture at the top. Such casts are likely to turn out bottom-heavy and pretty shapeless at the top.

Or, what if the clay fails to achieve a uniform thickness? Adding more water may smoothen out the clay slip; however, the excess water will waterlog the mold and cause the cast to shrink excessively. Such casts take too long to cure and may turn out cracked as well.

It follows that less water should be used so that the clay slip is workable. However, this will make the mixture thick, viscous and clumpy. So how can an artist use such a clay slip?

Magic of deflocculation

The answer to all these issues lies in a deflocculant. This material is added to clay to keep the particles from coalescing together.

A deflocculant magically turns a thick and viscous clay mixture into a thin and runny one, that too without adding any water. In effect, it works to reduce the viscosity of the clay particles thus giving it the right consistency. As the particles are suspended properly, this makes the clay slip smooth and easy to apply too.

While there are various deflocculants like sodium ash, sodium carbonate, barium carbonate, polyphosphates, etc, sodium silicate is the most commonly used deflocculant for clay slip. This product is not only effective but also economical and odorless and cures to a strong and rigid form.

How to use

Sodium silicate – also called water glass – is easy to use. Clay powder is mixed with a little water to form a thick paste. Then a few drops of liquid sodium silicate are added to the mixture. Once mixed properly, the clay slip starts becoming thinner. You can add more sodium silicate till you achieve the desired consistency. Using sodium silicate has a dual advantage as it reduced shrinkage as well.

However, after a certain level, sodium silicate starts having an opposite effect on the clay slip. That is, it will start flocculating or thickening the clay once again.

Yet, carefully monitoring the proportion of sodium silicate will yield the perfect clay slip.

The author is a mold maker by profession. He has penned the article down to highlight the uses of latex rubber in mold making and casting.