Clay is the main raw material when it comes to pottery making, but it can be defined as just dirt for that matter since it’s dirt which occupy most parts of the ground level, though clay is a different type of dirt which has elastic capability where it can be used to mold, the rocks which have decompose bring about the clay type of soil, other non-elastic earths are also coming about by the process.
The clay ability to be cohesive when in a wet condition makes it good for molding different shapes; however, the types of clay can be categorized by their level of maturity when heated under certain temperatures.
Earthenware clay type
The earthenware type of clay is the type which was there from an earlier times, the potters in the early days used to use it for molding in pottery, it’s more readily available almost anywhere, it has a characteristic of very sticky and plastic which can be easily molded in to any shape, it has a characteristic of being so sticky which makes it to hold once molded in to a shape, the earthenware clay has a large amount of iron which when heated to the temperature of between 950 degree Centigrade to 1100 degrees, it becomes hardened at such temperatures, it has red, yellow, grey and orange colors.
Stoneware type of clay are mostly plastic in nature, its color is grey when in a moist condition, when it’s subjected to firing its colors ranges from buff color to light grey shade, brown color to medium grey, the amount of firing will determine the fired colors greatly on this type of clay.
Medium fires or high level fires can be used when firing Stoneware clay type, medium fire is between 1160 to 1225 degree Centigrade, and much stronger fires range between 1200 to 1300m degree Centigrade to make the material mature and hardened.
The Ball Clays contains fewer mineral impurities and are highly characterized by plasticity, they appear dark grey in color when wet or moist, but turns to either dull buff or light grey when firing is done, the firing process to a full hardness and maturity is within the range of 1300 degree centigrade, but no matter how attractive they can look, this type of clay has a big setback, it has a high rate of breakage and shrinkage while fired, but their importance come when mixed with other clay types for more workability and plasticity.
Fire clay type
Fire Clays are known for their characteristic of high firing range, they mature to hardness at a temperature of about 1500 degree Centigrade, they contain very less mineral impurities, but have iron spots which when fired bring about speckled look on the end product, the type of clay are mainly used in other stoneware materials for a high rate of maturation, they are used to offer Fire Clay more rough surface or tooth, they are used in fire Kilns for extra packs which comes in handy to check temperatures in the process.
Kaolin/ Porcelain clay
Kaolin Clay are very free from mineral impurities making them ideal for porcelain, they have very light coloration when moist or when dry, their main colors are much lighter grey, but when completely fired they appear lightest grey, buff to white colors or almost white, the plasticity of Kaolin clay is very low making it difficult working with, they are always mixed with other types of clay for easy workability and temperature control, porcelains are mostly a mixer of Kaolin and Fire Clays, they mature at a temperature of 1800 degree centigrade which is the highest.
There is however other different types of clay and terminologies used, but the above mentioned sums up the major types of pottery clays being used today.Read more…