The plastic paste required for shaping consists of ceramic powders and water. Clay
is usually the main ingredient in the paste because it has ideal forming characteristics.
The more water there is in the mixture, the more plastic and easily formed is the clay
paste. However, when the formed part is later dried and fired, shrinkage occurs that can
lead to cracking in the product. To address this problem, other ceramic raw materials
which do not shrink on drying and firing are usually added to the paste, often in significant
amounts. Also, other components can be included to serve special functions. Thus,
the ingredients of the ceramic paste can be divided into the following three categories
[3]: (1) clay, which provides the consistency and plasticity required for shaping; (2) nonplastic
raw materials, such as alumina and silica, which do not shrink in drying and firing
but unfortunately reduce plasticity in the mixture during forming; and (3) other ingredients,
such as fluxes that melt (vitrify) during firing and promote sintering of the
ceramic material (feldspar is an example), and wetting agents that improve mixing of ingredients.