Clay is an extraordinary material with great applications that has been used in pottery and ceramics industry for thousands of years. That is what makes clay so special and pliable to be fashioned into useful and aesthetic items? Science has the answers to these questions, about the properties of clay.
What is Clay?
Clay is a fine-grained natural material that forms as a result of weathering and erosion of rocks for long periods and is used in art and pottery. Clay is a family of naturally occurring hydrous aluminium phyllosilicates known as clay minerals. They include kaolinite, montmorillonite smectite, illite and chlorite and are the most widely distributed and used types. Clay consists of small crystal platelets held parallel to one another which results in the layered atomic structure. Most importantly, clay is workable when wet: that is, it will not crack under pressure as many fine ceramics tend to do, and it becomes hard and almost ineradicable when dry or baked.
The Formation Process
Clay is an element derived from the weathering of rocks rich in minerals such as feldspar, mica, quartz, volcanic ash or lava. When these rocks are immersed in water, potassium, sodium, calcium, iron, magnesium and other components are disintegrated and soluble clays are washed away. These component over thousands to millions of years are deposited in lake or sea beds, or ancient soils through processes such as by rainfall, rivers or glaciations, wind, tides and the like. The deposited clay materials form a compact body in which the crystal structure can grow. It depends with the initial rocks that are present and the condition of the environment at the time of clay formation.
The Composition and Properties
As with most particles of clay, they are less than 2 micrometers in size, thus it has a high surface area to volume ratio. This means that the effects of the molecular interactions at the surface are singularly responsible for the overall phenomenon. There are different properties that are considered important, of which the cation exchange capacity (CEC) is one of the most important. Substitutes intrude in the crystalline lattice with vacancies that contain negative ions, which are offset by positive ions (cations), such as calcium, magnesium, sodium, potassium, and hydrogen. Due to this charge imbalance, clay can effectively capture and hold cations.
It also awards clay layer structure what is known as ‘surface reactivity’, the surfaces that dictate the chemical activity and bonding with water and other organic molecules. For instance, oxygen atoms are somewhat negatively charged, while hydrogen atoms are slightly positive. This polarity makes the compound form hydrogen bonds with polar water molecules.
Water is drawn into the interplatelet gaps from the laminated crystal platelets The interplatelet spaces are occupied by water molecules. The water that is added softens the layers, making it possible for the layers to move across one another without cracking as the clay deforms under shaping. During drying process water is drawn out and the clay platelets are shifted as the attractive forces pull them closer.
The Transformation Process
Clay can be directly extracted from deposits on the ground or it can be processed and remixed to possess some features. When acquired, this clay is subjected to a series of transformations to produce a hardened decorative product.
- Wedging –Wedging means slicing the clay and then slamming it to force out all the air trapped in a lump of clay and to provide an even texture. This assists in preventing cracking and exploding during the subsequent firing stage.
- Shaping – Clay is modeled or built by hand, modeled from a block of clay by using hands, wheel or through casting, extruded or thrown on a wheel. Clay is describes as being able to be pinched, coiled, pulled upwards and can be pressed into or draped over a mold. It partly orients the clay platelet structure in the shaping process.
- Drying & Greenware – Wet clay shaped pieces are allowed to air dry slowly to avoid cracking until they get to a state that is referred to as dried clay or greenware or leather hard state. This is the time when extra molding can be incorporated before the sculpture is completely dried.
- Bisque Firing – Raw greenware is the porous clay that goes through the first heating at a temperature above 1000°F in a kiln. This bisque firing process partially melts the clay platelets while burning off any residual water to create the hard shape on the clay platelets in the form of the required shape of the decorative plate.
- Glazing & Decoration – Glazes are those which are made from a solution of glass like silicate compounds floated in water and are applied by brushing, dipping or spraying. Opacifiers are coloured oxides such as cobalt, copper, and manganese which produce strong coloured surface effects. Glazes on the other hand, act more as a coating that melt and fuse on the surface of bisqueware during firing. Other related elaborate procedures that can be made to the surface of a ceramic piece include carving, burnishing or painting.
- Final firing – This takes in heating the clay bisque to over 2,000°F depending on the type of clay to be used, where the clay platelets and glazes become fused and vitrified to make a dense glass-like substance that cannot be penetrated. The last firing alters and petrifies the ornamented ceramic body in the process of creating a decorative ceramic object.
Clay’s Transformational Nature
One has to wonder what feature makes clay so special: due to the plasticity of the material, it can be modeled into any given form while still wet and will solidify in the assumed shape when properly fired. These characteristics, such as, hydrous nature and the layered surface reactivity facilitate molding without cracking when dried. It then ‘freezes’ the structure by causing the lattice to sinter and become vitreous. This forms the basis of the conversion from a raw and natural material form of clay into a useful, aesthetically and permanently useful ceramic object. As much as it is applied in functional and aesthetic pottery, the mastery of clay science comes in handy in the making of these objects.