Potters understand how difficult it is to produce a single piece of work. But once fired, it cracks. This means understanding the causes to prevent them effectively.
Cracking in ceramics can occur both before and after firing, with different types of cracks. Pre-firing cracks tend to be rounder because at high temperatures, both the glaze and the clay body melt, making the crack's edges less sharp. In contrast, post-firing cracks, which occur after the highest temperature has been reached, become very sharp as the piece cools and its structure changes.
Pre-firing cracks can occur during clay preparation, forming, drying, movement during glazing, and the pre-heating stage of firing. However, post-firing cracks during the cooling stage are caused by firing too quickly, especially during quartz inversion.
- Cracking from raw materials: The raw materials used to make ceramics can be divided into plastic materials and non-plastic materials. To create a good clay body, the proportions of both must be calculated appropriately for the forming process and the properties of the fired product.
- Cracking from clay body formula: If the potter miscalculates the clay body formula from the beginning, the chances of cracking problems will increase.
- Cracking from raw material preparation: Even if the formula is well-calculated, if the clay and water proportions are not precisely checked against the formula before mixing or if they are not kneaded well, the well-thought-out formula may not yield the desired results.
- Cracking from press forming: Press forming requires high pressure to compress low-moisture clay powder into a stable shape with sufficient green strength. Therefore, when the greenware is pushed out of the mold, it expands in all directions, which can cause cracks during this process. Additionally, if the clay powder used for pressing has low moisture content or poor particle distribution, it can also lead to cracks.
Furthermore, cracks can also arise from glazing and decoration, as well as firing, which means potters must always consider many environmental factors such as glaze weight, piece thickness, moisture, firing time, etc. Therefore, potters should thoroughly understand the causes of cracks to keep all processes up to standard and achieve beautiful, desired results.