Salt was formerly expensive and available only in soy sauce and preserved foods in ancient China. In Hong Kong, several forms can be found. Table salt is the finest ground and is less frequently used. Many chefs and cooks use sea salt, which has a greyish cast and coarser texture than fine table salt. This sea salt is frequently found in bins at the Hong Kong markets. Rock salt is known best for its role in freezing ice cream and the larger crystals make an excellent medium of heat conduction. Rock salt is also used in certain kinds of Hong Kong—Hakka cooking, such as with chicken or squabs.