Certain Sui and early T'ang white wares are regarded as the world's earliest porcelains. Such desired qualities as hardness, whiteness, and translucence can all be found in 7th-century white wares from the Hsing and Kung-hsien kilns in Hopei province. This northern region had accessible deposits of kaolin (a fine white clay) and feldspar, which are essential ingredients for porcelain making. At other kilns, a slip was widely used on monochromes, particularly white wares, to mask clay imperfections and provide a clean, uniform surface for glazing. Hsing wares, however, were of such high quality that these slip coatings were unnecessary. Northern white wares appear to have been made in great quantities and proved popular with a broad clientele. For a while they even eclipsed the older preference for celadons. In fact, T'ang white wares-durable, finely potted, and unadorned-set a technical and aesthetic standard for all subsequent dynasties.