Pottery is clay that has been formed into a shape, dried, fired and then glazed and can be a decorative or practical vessel. Clay is a natural product dug from the earth, a product resulting from the decomposition of rock within the earth’s crust during millions of years and this decomposition occurred when water eroded the rock, breaking it down. In the past, many ceramic firms were based in certain locations because the earth there was suitable for making clay and each firm went through the whole process, from digging out the clay to selling the finished products. The clay was dug out of the ground, mixed with water and screened to clean, removing all insoluble material. The water was filtered off the clay and the clay was left until it reached a semi-dry state, after which it was cut and separated into large blocks and stored in caves, sometimes for up to two years, as ageing helps to assist the plasticity.
Before being used, the clay has to be well kneaded to form a smooth plastic body for throwing and molding tiles, pots and plates. For the first firing, the pieces have to be left until the clay is bone dry. The firing of clay should start slowly, to allow it to completely dry out until it reaches 600ºC, when it turns into a ceramic. The firing continues until it reaches the required temperature for the type of clay being used. There are many different types of clays, with different colors, textures and different firing temperatures and the higher the temperature it can be fired at, the stronger it becomes. Products in clay can be formed in many different ways, with the potter’s wheel, molds, sculpture and cut or stamped into squares or slabs and they can be decorated by shaping the clay with different techniques, fluting, drawing, coiling, indenting, etc.
Clay, when fired, changes into a material that is solid, breakable but still porous and is known as bisque. The firing can be carried out using two different methods, slip firing, when the clay and colors are fired together in one firing or bisque firing, when the clay is fired, becomes bisque, is then decorated and fired again. Each of these methods has many variants and it is the glaze in the slip and the decorating that make the clays vitreous.