Clay is easier and better to use when it has aged in the damp state. This means leaving it in a damp place a box or crock for a period of a week to two or three months, the longer the better. Follow the article to know more about for the preparation of clay.
So long as the clay is moist, it is very plastic and easy to work. If it is pushed, it moves readily and stays in the new shape. If a piece of clay is added to the original piece, it is only necessary to lay it firmly in place and work it into the mass with a finger or tool. But once the clay has hardened, it is practically impossible to add moist clay to it.
Clay shrinks as it dries. Thus, when moist clay is added to the semi-dry body, the moist clay shrinks more, and the unequal shrinkage causes it to crack and peel. Good modeling clay normally shrinks about one inch to every 12 inches during the processes of drying and firing. Half the shrinkage takes place while the completed model is drying, the other half takes place in the kiln.
Slip, or liquefied clay, to be used for casting objects in molds and for modeling and decorative purposes, can also be purchased in prepared form. Basically it is clay and water with some other chemicals added to produce certain definite effects. The chemicals used in slip are called deflocculants. The purpose of a "defloc" is to form a liquid clay without using too much water. In plain language, a deflocculant is "water wetter". That is, a small amount of liquid is made to perform the function of a larger quantity. The principle involved is that an alkaline water can hold more clay than an acid one. It separates the clay into finer particles so that they are held in suspension or a colloidal state.
Castings can be made of slips that do not contain a defloc. But it takes far longer for the mold to absorb the extra water, and the results are rarely as satisfactory. Special casting bodies may be purchased in powder form. The amount of water to add and the directions for mixing are given by the manufacturer. Common deflocculants are potassium carbonate, sodium gallate, sodium tannate, and a combination of sodium carbonate and sodium silicate (waterglass).
If you prefer making your own casting slip, rather than buying it ready mixed, take about 10 pounds of powdered clay and add five pints of water and one teaspoon of potassium carbonate, or any other de-flocculant. Mix well and let stand overnight. Stir for a few minutes each day for several days. Your greatest plague will be air bubbles, which must be removed from the slip by stirring and banging. After the slip has been seasoned for one week, strain through a 60- or 80-mesh sieve. A good slip has the consistency of honey.
Many chemicals can be put in use for making your clay better. But instructions must be followed property in order to avoid any future side effect on your model.
Article Source: http://www.artsymmetry.com
Mitch Johnson is a regular writer for www.curtains-n-drapes.com/. His articles have also appeared on www.ceramicsmadeeasy.info/ and www.ceramicsmadeez.info/
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