104 FLORIDA GEOLOGICAL SURVEY-I5TH ANNUAL REPORT

 CHAPTER VI

 KINDS OF CLAYS AND THEIR USES

 This discussion of the kinds and uses of clays is based upon the commercial classification and is in no way related to their geological occurrence or origin. The use of any one clay, moreover, is not always restricted to the general type of ware mentioned here, but may be employed for other purposes as well. For example, a stoneware clay may be used for roofing tile or terra-cotta, but its chief value lies in the fact that it is adapted for the manufacture of stoneware.
 KINDS OF CLAY
 Kaolin-This term was formerly used to include only a refractory white-burning residual clay composed mostly of silica, alumina, and chemically combined water with a low percentage of fluxing properties, but now include some sedimentary clays of similar physical properties. Kaolins have a low air-shrinkage, low modulus of rupture, low bonding power, and their plasticity is commonly poor. They are used chiefly in the manufacture of high-grade white wares:
 Ball-Clay-A ball-clay is a plastic white or nearly white-burning sedimentary clay of high refractoriness and bonding power. The airand fire-shrinkage is frequently high. Ball-clays are used chiefly in the manufacture of white ware to increase the plasticity, bonding strength and density after firing.
 Fire-Clay-A fire-clay is highly refractory, fusing above cone 27, of variable plasticity, porosity, shrinkage, transverse strength, and color and has a low percentage of iron, alk-ali-es, hme,, magnesia, and titanium.
 Stonezuare-Clay-A son'evreftay is'-bf "gdo plasticity, medium to high transverse streiih fair toughness, and 's1 d bcbtirn dense at a comparatively low ,tbiipenature (cones 6-8). Its color is tieit11mportant but is preferably-gray, cream' -,rt0ug f :' f ohldi be fine-gr 'ined, of smooth, even te,'ure, and should 6ihe' Vdl'wxs tinkage and gobd vitri-fying qualities. Most modern stoneware, however, is made from a blend or mixture of several clays. Stoneware clays are also often used in the manufacture of other types of products, as art ware, earthenware, roofing tile, and terra-cotta.
 Terra-Cotta Clays-Clays for this purpose should be semi-refractory, of fair plasticity, high transverse strength, high bonding power.