Pot Web: clay and fire

Clay and Fire

These two elements are not only basic to all civilisations, they have both been known to all eras at different times throughout "recorded" history and sometimes pottery production has itself been that method by which that history has been recorded [explore the information that can be gleaned from the close study of Greco-Roman vases and the "story" they depict]. Consequently, we can find Ceramic artefacts - pottery for use, religious purposes and a culture’s artistic expression - scattered through the World’s peoples during the past, almost, 5,500 years. To put this in perspective, we can discover pottery from pre-dynastic Egypt (3,500 BC); in China during the Kansu period (3,500BC); Europe during the Cretan period (3,000BC) as well as in South America during the pre-Colombian era. As well as understanding the historic spread of Pottery, it is valuable to note where and when the different types of ceramics were being produced. Important because this gives us a true and realistic understanding as to what can be achieved and accomplished in our own pottery endeavours - that is, if it worked in a certain way 5,000 years ago, chances are that it can also work in the here and now.

The simple historic map above provides us with clues, in understanding the scope of pottery. In appreciating this we need to be clear on two crucial matters. Firstly clay is clay is clay, is not correct. And neither is the statement, "A pot is a pot is a pot". Different clays produce different pots and for many, many very different purposes. Secondly, because the Earth is endowed with many types of clays, we need to appreciate how clay has been formed - it’s Geology. Understanding this will give us a "basic" appreciation of what we can do with this remarkable material and more importantly, be confident how the final product could be used, how it will perform and consequently our success in producing a long-lasting article.

So, for the purposes of pottery production the geology (clay formation) and variation (clay location) of clay/s is tied into the "use" of particular clays. There is also the technological-historic perspective, which provides us with clues as to how the different civilisations have adapted this material to their purposes and how those same civilisations had adapted and adopted "new" Ceramic technologies to achieve what they wanted.

Being formed from the granite-type igneous rocks, the raw materials of pottery constitute the vast majority of the Earth’s crust. This hard igneous rock had been deposited on the surface of our Earth by hot gasses bubbling this material to the surface producing a "softer" rock, containing "feldspatic" minerals. Millions of years of exposure of this soft rock to weathering by rain, and variation of heat and cold broke these feldspars down into firstly "Primary" clays, resulting in them being deposited close to their source of the original hard rock or "granite" [the water soluble free "salts" being washed away] . Clay, travelling further down river to the open sea, and being "mixed" with other minerals and settling-out, produced "Secondary" clays [As an aside, it is worth noting that the salts that had been leeched from the original Granites, having found their way to the newly formed seas, is the reason why the Seas of the World are in fact "salty"!]. The primary "China" clays or residual clays allow the potter to produce high-fired ware and the "Secondary" or sedimentary clays provide the potter with low firing earthenware. Of course within these two broad definitions, there is a vast range of different clay "types". Mixing different clay types together, the potter can "adjust" these clays to fit the type of production and product wanted. It is also worth noting that what a potter is almost doing is re-sintering or recreating the original granite formation from the "glassy" silicate and aluminous products, originally brought to the surface of the Earth, all those millions of years ago!