Clay Questions - Potclays Ltd.

My clay is too hard - how can I soften it?

It should be remembered that some clays are 'thixotropic'. Oxide-heavy clays such as red and black clays are more thixotropic than others. For… Read More About This Question

How can I make my pieces frostproof?

Pottery is damaged when moisture that has been absorbed into the clay, freezes. Water expands as it freezes and the force of this expansion ca… Read More About This Question

How should I safely handle powdered ceramic materials?

Dust from powdered ceramic raw materials, glazes, slips and clay can cause health problems if not properly controlled. The Health and Saf… Read More About This Question

I've fired my vases to vitrification so why is moisture still seeping through them?

In the vitrification process the free silica and feldspathoids in the clay melt and flow into the gaps between the clay particles, welding the… Read More About This Question

Does Potclays clay contain sulphur?

This is a question we are asked quite often. There are trace amounts of sulphur in most ceramic clay bodies. It is at its highest level in bod… Read More About This Question

How can I improve 'toasting' in my fired clay body?

Toasting in the unglazed clay surface can be encouraged by having a thicker cross section of ware, slower drying and higher temperature f… Read More About This Question

What's the maximum firing temperature for your clay bodies?

This is approximately indicated by the vitrification point stated for each clay in our catalogue but, with stoneware, it will be lowered by re… Read More About This Question

What's the recommended firing process for clay and glazes?

We generally recommend biscuit firing at 1000-1060C then following with a glaze firing to a higher temperature which matures both the clay and… Read More About This Question

What is the optimum firing rate to use?

The optimum rate depends upon the thickness of the pots and clay type e.g. thin cast and grogged bodies can be fired quicker than thrown and u… Read More About This Question

What can I do if my clay has frozen?

Clay that has been "lightly-frosted" (that is to say, the freezing has been limited to the surface) is unlikely to suffer adverse ef… Read More About This Question

How much clay do I need for my mural?

We have a handy calculator here on our Technical Information page - direct download link here>… Read More About This Question

Can I use items made from your flecked clays in the microwave?

Yes - the fleck in our clays is created by an iron-bearing compound which is not metallic therefore will not reflect the microwaves.… Read More About This Question

Why is my bag of red clay so stiff compared with other types of clay?

Potclays red clay bodies are manufactured to a hardness (NGK reading) of between 6-8, tested with an industry-standard penetrometer … Read More About This Question

Can I mix two or more clays together?

In the majority of cases the answer to this question is yes, it is possible to mix clays together to produce a composite clay with intermediat… Read More About This Question

Why is my fired ware weak and brittle?

This is normally a very good indication that the ware is underfired. All fired clays develop increasing strength as the firing temperature inc… Read More About This Question

Why doesn't Potclays have a system in place to accept clay bags for refilling?

Logistical Difficulties: All our clays are bagged straight from the pug to optimise condition and shelf life. Stock availability of used bags… Read More About This Question

When should I clean out my sedimentation tank?

Sedimentation tanks should be cleaned out regularly to prevent the sediment level building up (and also preventing odour). The higher the leve… Read More About This Question

What’s causing the white bloom on my red clay pieces?

The white bloom that sometimes develops on the surface of unfired red clay bodies is as a result of soluble salt deposits in the clay migratin… Read More About This Question

What is the ideal bisque firing temperature to use?

The biscuit firing temperature that is chosen should either give the clay sufficient strength to withstand the glazing process, or fire t… Read More About This Question

What is the difference between stoneware and earthenware?

The most obvious difference between stoneware and earthenware is temperature, stoneware pots are fired above 1200°C and earthenware is fir… Read More About This Question

What does your "recommended firing range" mean?

The "recommended firing range" is the temperature range over which we expect the clay to have a good glaze fit, with no crazing or peeling. Ea… Read More About This Question

Is a bisque firing necessary, or can I skip straight to glaze firing?

Both the clay and glaze, particularly in the case of stoneware and porcelain, can be matured in the same firing quite successfully. However, g… Read More About This Question

How should I keep my work damp in-between sessions?

It is possible to keep clay in a workable condition almost indefinitely as long as it is kept moist. This is usually achieved by wrappin… Read More About This Question

Does "Bisque" mean the same thing as "Biscuit"?

Although today these terms are practically interchangeable in the description of the first firing, they originally had different meanings and … Read More About This Question

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