Sapphire is used in the dinnerware, artware and tile industries. Some books cite the presence of some free silica in kaolin as a silicosis hazard, however other sources and regulatory bodies recognize no known hazards and consider it a nuisance dust. It isn't possible to be allergic to an inert mineral like clay. However molds, mildews, and other organisms that can make their home in clay, along with their byproducts, can cause a problem. Kaolin is pure clay mineral.
Kaolin is the clay of choice for any clay body which needs to be clean and white.
Many porcelains contain only a kaolin mix as their clay complement. However, most kaolins have relatively low plasticity when compared to ball clays, earthenware and stoneware clays. Thus in non-casting bodies it is often not possible to achieve enough plasticity employing kaolin alone. Additions of ball clays, bentonites and other plasticizers are thus common where translucency and whiteness are not paramount. Kaolins are whiter and cleaner than other clays because they are mined near the site where they were weathered and altered from the parent rock.