Meissen porcelain further precaution, very few workers knew the special secret ("arcanum") of how to make porcelain, and then perhaps only part of the process. Thus, for a few years, Meissen retained its monopoly on the production of hard-paste porcelain in Europe. By 1717, however, a competing production was set up at Vienna, as Samuel Stöltzel sold the secret recipe, which involved the use of kaolin, also known as china clay. By 1760 about thirty porcelain manufacturers were operating in Europe, most of them, however, producing frit based soft-paste porcelain. In order to identify the original Meissen products, Meissen developed markings that
Porcelain coloured, translucent (except when of considerable thickness), and resonant". However, the term "porcelain" lacks a universal definition and has "been applied in an unsystematic fashion to substances of diverse kinds which have only certain surface-qualities in common". Traditionally, East Asia only classifies pottery into low-fired wares (earthenware) and high-fired wares (often translated as porcelain), without the European concept of stoneware, which is high-fired but not generally white or translucent. Terms such as "proto-porcelain", "porcellaneous" or "near-porcelain" may be used in cases where the ceramic body approaches whiteness and translucency. A high proportion of modern porcelain is made of the variant