keramik88

Archive for the ‘ceramic ( English language )’ Category

Clay, the Driying and Firing proses
Many potters, especially beginners, use prepared clays without much thought. However, there comes a point when it is useful to understand the process that clay goes through during drying and firing. This can help troubleshoot many of the problems you experience with your pieces. Plus it is darn interesting!
Air Drying
Wet clay contains a large amount of water, a minimum of 25% water. When clay starts to dry, water evaporates from it. As this happens, the particles of clay are drawn closer together resulting in shrinkage. Many problems with clay are formed by uneven rates of drying, which create stresses in the clay. Sometimes these stress show up right away as cracks or warpage, other times not until during or even after firing. So it is important to ensure drying is even. This is done by ensuring uniform thicknesses throughout the piece, drying slowly, and even slowing down the drying of certain parts. This has been discussed in several previous tips. Read the rest of this entry »

RAW MATERIALS

RAW CLAYS
The theoretical formula for clay is Al2O3 2SiO2 2H2O, an alumina-silicate, but none are that pure and uncontaminated. There are many technical characteristics that define a material as a clay but, for ceramics, the primary characteristic beyond the alumina and silica content is the fact that they are composed of very small flat platelids with a resulting very large surface area with microscopic water between them so they slide on one another and additionally tend to hold their shape. Additional properties of clays are 1) harden when dried and become permanent when fired, 2) shrink during drying and firing, 3) refractory (resist softening at high temperature), 4) heat, sound and electrical insulation. Read the rest of this entry »