Porcelain is made from clay, but the specific type of clay and other ingredients distinguish it from ordinary ceramics. Production begins with kaolin, a specific white clay, which is mixed with other naturally occurring minerals to form the ceramic body. This combination allows the material to achieve its qualities of strength, whiteness, and translucency after being fired in a kiln. The final product is a durable, glass-like material fired at high temperatures to achieve a transformed structure.
The Unique Composition of Porcelain
The fundamental difference in porcelain production lies in its primary clay component, kaolin, also called China clay. Kaolin is a pure, soft, white clay mineral that is finer and whiter than the common clays used for earthenware. This purity, specifically its low iron content, is necessary to achieve the brilliant white color that characterizes true porcelain.
Two other components are required to create the porcelain mix alongside the specialized clay. Feldspar acts as the flux, which is the melting agent in the composition. When the material is fired, the feldspar liquefies at high temperatures, creating a glass-like liquid that flows and binds the other particles together.
The third component is quartz, which serves as the skeletal filler in the raw mix. Quartz provides the necessary structure and stability to the porcelain body before and during the firing process. A typical hard porcelain composition is approximately 50% kaolin, 25% feldspar, and 25% quartz by weight, though these ratios can vary.
The Process of Vitrification
The transformation of the raw porcelain mix into its hard, finished state occurs through a process called vitrification. Vitrification is the fusing of the ceramic body into a dense, non-porous, and glass-like structure. This process requires the ceramic to be fired at high temperatures, typically ranging from 1,200°C to 1,400°C.
During the heat of the kiln, the feldspar flux melts, filling the spaces between the kaolin and quartz particles. This molten material binds the rigid particles together, and as the porcelain cools, it solidifies into an amorphous, glassy matrix. The resulting structure has low porosity, often near zero, which makes the porcelain impermeable to water without needing a glaze.
Vitrification is responsible for several of porcelain’s defining characteristics. It imparts high mechanical strength and hardness to the material. The fused, glassy structure allows light to pass through thin sections, giving true porcelain its signature characteristic of translucency.
How Porcelain Differs from Other Ceramics
Porcelain is categorized separately from other common ceramics, such as earthenware and stoneware, based on its material purity and firing intensity. Earthenware is made from common clays that contain more impurities, such as iron oxides, and is fired at a lower temperature, usually below 1,150°C. This lower firing does not cause the body to vitrify fully, resulting in a product that remains porous and absorbs water unless it is covered with a glaze.
Stoneware represents a middle ground, as it is fired at higher temperatures, typically between 1,150°C and 1,300°C, which causes it to become partially vitrified and non-porous. Stoneware uses less refined clays than porcelain, meaning it lacks the pure white color and the translucent quality of the final product.