Cracks In Pottery: Why They Happen And How To Prevent Them
Once the stain pigments are prepared, they can be used to mix in the clay or mix in the clay water to prepare the colored clay water for decoration directly using in the amount of 0.5 - 3 % of dry clay weight. Mixing the colors in the clay preferably by adding stain pigments to the mixture in the last hours of clay preparation by wet grinding method after approximately 90% of the total grinding hour. Then add the color until the mixture is well combined until the end of the grinding period. However, some stain colors may be used for both glaze and clay, but in general stain colors used on clay do not fuse well when used as Glaze Stain
All potters understand how difficult it is to produce a single workpiece especially when it's cracked after the firing is completed. Therefore, it is important to understand its cause in order to prevent it from happening.
Ceramic cracking can occur both before and after firing and they can be different. The cracks occurred before firing will be more rounded due to the high temperature. Both the glaze and the clay will melt causing the wound of the crack to be not very sharp which is different from the cracks occurred after firing that has passed the maximum temperature range. When it cools and the structure is changed, the cracks will not be very sharp.
However, the cracks before firing can occur since the preparation of the clay, forming, dry cycle, movement during glazing including the range pre-heating of the firing but the cracks occurred after the firing during cooling that is caused by firing too fast especially during Quartz inversion
- cracking from raw materials Raw materials used to make ceramics can be divided into (Plastic materials) and (Non plastic materials) In order to make good clay mixture, the proportion of both must be calculated according to the molding process and product properties after firing.
- Cracking from clay formula If potters miscalculated the clay formula in the first place, the chance of causing cracking problems will be greater
- Cracking from raw materials preparation Even if the formula is well calculated but if the proportion of both clay and water is not measured exactly according to the formula or the mixture is poorly combined, a well thought out formula may not produce the desired result.
- Cracking from compression molding Compression molding requires high compressive strength in order to compress the clay powder with low moisture content to be able to maintain its shape and raw strength reasonably. Therefore, when the raw workpiece is pushed out of the model, it expands in all directions. This leaves the opportunity for cracks to occur in the meantime. In addition, if the compacted clay powder has low moisture content or poor dispersion of the clay grains, it can also cause cracks.
Cracks can also occur from glazing and finishing, as well as firing, so potters must take into account many environmental factors such as the weight of the glaze, the thickness of the workpiece, humidity, time, etc. Therefore, potters should understand causes of cracks well in order to control every process to be in the standard to get a beautiful piece of work