It is the process of exposing ceramic products to high temperatures for conversion into durable pieces. During firing the clay and glaze are hardened to make it impervious, unlike the unfired clay which is more porous and may be absorbable. In some cases fired pieces can still absorb moisture but this will have no adverse effect on the products.
If an experienced potter carefully controls the firing factors, such as the rate at which the items are heated and cooled, the presence of other materials in kiln, and the amount of oxygen in the kiln, they can achieve a wide range of effects. Most times products are fired at different temperatures for the potter to attain the desired results. High-fired clays tend to be impervious and durable.