After several weeks of receiving many questions from Clayoven visitors regarding where to find clay and specifically what type of clay one should buy from potters suppliers, I decided to ask an expert.
Sue works at Pottery Ceramic Services (the Kiln Engineer – a supplier of all things pottery related based in Fordingbridge, Hampshire,UK) and knows a lot about pottery clay (useful in her profession I guess!). Last week I cheekily asked her if she would like to write a small post for the blog about different types of pottery clay and she kindly said yes. This is what she had to say:
There are 2 main varieties of clay, Earthenware or Stoneware. This divide is depending on firing temperatures. Earthenware clay is fired in a kiln at a lower optimum temperature (maximum of approximately 1160ºC) and Stoneware clay is fired at a much higher optimum temperature (maximum approximately 1280ºC)
For building a Clay/Pizza oven, although the clay is not going to be kiln fired, the heat from the actual firing is enough to heat the clay right the way through, so Earthenware clay is the usual clay to purchase.
Prepared clay bought from a pottery supplier will be ready to use, all impurities such as stones etc. will have already been extracted. The last thing a production potter wants to do is mess around with the clay in the first place making it fit for use! So it will have gone through a process of pugging and will be ready to use straight from the bag.
Pottery clay comes in many different colours and grades from a very fine clay for detailed sculpture work to what is known as a heavily grogged (particles of already fired clay) clay which is suitable for hand-building, and this is what I would suggest for the Clay Ovens. Grogged Terracotta Clay is mostly sold for the making of Clay Ovens as it has about 10% grog and when the clay has dried out, and has been fired through, is a lovely warm colour. Extra grog or sand may be added to the clay if required, although many people use it just as it is with good results [I would still reccommend that you use a sand/clay mixture for your oven at the normal ratio of 2:1 sand:clay, grogged or not! - Simon].
Clay is usually sold in 12.5KG packs and depending on the size of Oven required may take 10 – 15 bags to complete the project [I cannot verify this becuase firstly I didn't buy clay for my oven and secondly I never weighed out the actual amounts I used - Simon].
So now you know. How fabulous is that – thanks so much Sue!
Of course, in the interests of fairness I would add that there are other pottery suppliers out there who will also supply you with potters clay. However, I’m sure none of them will be as super friendly as Sue and the team at Pottery Ceramic Services. In return for her aticle I promised Sue a gratuatous plug, so if haven’t done so already, here you go!
POTTERY CERAMIC SERVICES,
UNIT 2 ARCH FARM INDUSTRIAL ESTATE,
HAMPSHIRE. SP6 1NQ.
TELEPHONE NUMBER 01425 655540
EMAIL ADDRESS firstname.lastname@example.org