What You Need To Know About Porcelain

Peter Pugger has done some extensive research on porcelain clays and pug mills. Here are some helpful tips to think about if you're working with porcelain clay...

There are a wide variety of porcelain clay bodies on the market today. Porcelain clays are derived from numerous geographical locations, formulated with variable compositions and mixed together with a wide range of water chemistry. How do these factors play a role in the performance of the clay?

Some porcelain clay bodies are made up of specific elements that tend to leach alkalies. As the alkalinity (pH level) of the porcelain rises, the porcelain particles begin to deflocculate or reject each other. In turn, the porcelain becomes “short”.

Another problem that may occur as the alkalinity of the porcelain rises is the effect it has on aluminum. Under stable pH conditions (4.5 -8.5), aluminum has the ability to form an oxide layer that allows it to be highly resistant to weathering in industrial atmospheres where other metals break down. However, when the pH level rises above stable pH conditions, the oxide layer is unable to renew itself fast enough, causing corrosion or “pitting” of the aluminum.

The Solution is Simple!

Just add salt! Adding Epsom salt to the porcelain will raise the plasticity as well as eliminate the corrosive environment sometimes created by porcelain. How so?

Epsom salt is a acidic solutions that lower the pH level of the porcelain. As the pH level drops and the porcelain neutralizes or even becomes slightly acidic, the ions become independently charged. As a result, the porcelain particles attract one another (flocculates) which increases the plasticity. This also occurs naturally when clay is “aged”. As the clay begins to develop bacteria (mold), the bacteria produce acidic byproducts causing the pH level to drop and the plasticity to rise.

By lowering the alkalinity level of the porcelain, the aluminum now has the ability to maintain a suitable oxide layer which protects the metal from corrosion. Having a better understanding of porcelain and the benefits as a result of maintaining the pH level will go a “long way” in resolving plasticity and corrosion issues.

Below is a general rule of thumb when determining the amount of solution necessary to lower the pH level of porcelain. Though the figures may not be the exact measurement, we have yet to find a down-side to a slightly acidic pH level.

Epsom salt: 44 grams of Epsom salt per 25lb bag (moist) clay.

Mix w/warm water to dilute.