Clay in a plastic state still contains water so easily formed into ceramic objects. After drying the ceramic object will experience shrinkage. This happens due to the evaporation of water and water forming on the membrane surface of the body and ceramic objects, causing the clay granules become close to one another.
Clay will experience twice the shrinkage, the shrinkage which occurs from the wet into the dry state, called dry shrinkage and shrinkage that occurs during the combustion process, fuel is called shrinkage. Total percentage shrinkage (shrinkage and shrinkage of dry fuel) required preferably between 5% -15%.
Clay soils have a variety of different depreciation, the higher the plasticity of clay, the higher the depreciation. Too plastic clay percentages usually have more than 15%, so if the clay is formed will have a risk of cracking or breaking high. Depreciation clay that is too high can be improved by reducing or adding ball clay fire clay or grog.
Singkawang clay shrinkage of West Kalimantan plastic condition, dry, and biscuits shown in the picture below started.
Shrinkage of clay through the drying process and the combustion process can be seen as shown below.
The amount of dry shrinkage rate and shrinkage percentage of fuel can be calculated by the following formula:
plastic length – long dry
Dry shrinkage length = X 100% plastic
plastic length – long burn
Losses fuel = X 100% long plastic