Hard-paste porcelain is the original Chinese porcelain formula, built from kaolin, feldspar, and quartz alone, fired hot enough to vitrify all three into a dense, white, translucent body without needing any additional flux like bone ash or glass.
Hard-paste porcelain's kaolin supplies whiteness and refractoriness, feldspar acts as the flux that lets the mixture vitrify, and quartz (silica) adds structure and helps control shrinkage. Because none of these ingredients lowers the melting point especially aggressively, hard-paste porcelain needs a genuinely high firing temperature, typically cone 10 or above, to reach full vitrification; pushed to full maturity, this is what gives it its characteristic strength, whiteness, and translucency in thin sections.
Reaching that point takes two separate firings. An initial biscuit firing, typically 800 to 1000°C, hardens the unglazed body enough to handle and glaze safely without yet vitrifying it. The glost firing that follows, typically 1350 to 1450°C, is where the glaze itself fuses and the body reaches full vitrification at essentially the same time — a higher glost temperature than soft-paste porcelain or bone china ever reach, since both of those formulas are built to mature at a lower temperature instead.
Hard-paste porcelain is the formula Chinese potters, concentrated for centuries at Jingdezhen, developed and refined (see porcelain's own history), and the one European manufacturers spent generations trying to reverse-engineer without success. The breakthrough came at Meissen in Saxony: working with alchemist Johann Friedrich Böttger, scientist Ehrenfried Walther von Tschirnhaus determined that firing temperature mattered as much as ingredients, and by 1708 Böttger had produced a working hard-paste body from local kaolin. The first firing of true European hard-paste porcelain succeeded on 15 January 1708, and the Meissen factory itself was formally established on 23 January 1710, the first successful European hard-paste porcelain manufactory.
Hard-paste porcelain's narrow firing range and high peak temperature make it less forgiving to fire than soft-paste porcelain or bone china, both of which reach translucency at a lower temperature by relying on additional flux. It remains the standard against which the other two are usually compared, and is still the formula behind most fine Chinese and continental European porcelain production today.