Porcelain is built on three raw materials: kaolin for whiteness and body, feldspar to melt and bind, and quartz for structure. How pure they are, and how well they are balanced, sets the limit on everything the kiln can achieve.
Pick up a plate and you are holding a decision made months earlier, when someone chose what went into the clay. Glaze and firing get most of the attention, but the body underneath is where a porcelain’s character begins.
Kaolin: the white clay
Kaolin, also called china clay, takes its name from Gaoling, a hill near Jingdezhen in China, the city that made porcelain famous. It is a fine, white clay made mostly of the mineral kaolinite.
Kaolin gives porcelain its whiteness and its ability to be shaped. On its own, though, it is stubborn: it needs very high temperatures to mature and it doesn’t melt easily. That is where the other two ingredients come in.
Feldspar: the flux
Feldspar is a mineral that melts at high temperature. In the kiln it turns into a glassy liquid that flows between the clay particles and, as it cools, binds them together. Potters call this a flux.
Without enough flux, the body stays porous. With the right amount, it fuses into a dense, glass-like whole. This is the heart of vitrification.
Quartz: the structure
Quartz, or silica, acts as the skeleton. It helps the body keep its shape during firing, controls shrinkage and contributes to the glassy phase that makes porcelain hard.
A classic textbook porcelain is roughly half kaolin, with feldspar and quartz making up the rest. Every maker adjusts that balance.
Why purity matters
Impurities show up in the finished piece. Iron, for example, can tint a body grey or cause dark specks. Uneven particle size can leave weak points. A poorly balanced recipe may never fully vitrify, however hot the kiln.
That is why two plates can look alike in a shop and behave differently after a year of use. The difference was built in at the start.
How this shapes VITRO
We treat the clay body as the foundation for everything else. It has to be capable of full vitrification at approximately 1,250°C, carry a glaze made to meet international food-contact requirements, and stand up to daily use.
Next, see what happens to these materials in the kiln: Vitrification, explained.
