104 FLORIDA GEOLOGICAL SURVEY— I5TH ANNUAL REPORT 
CHAPTER VI 
KINDS OE CLAYS AND THEIR USES 
This discussion of the kinds and uses of clays is based upon the com¬ 
mercial classification and is in no way related to their geological occur¬ 
rence or origin. The use of any one clay, moreover, is not always re¬ 
stricted 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 air- 
and 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, alkalies, lime, magnesia, and titanium. 
Stoneware-Clay —A stoneware clay is of good plasticity, medium 
to high transverse strength, fair toughness, and should burn dense at a 
comparatively low temperature (cones 6-8). Its color is rather important 
but is preferably gray, cream or buff. It should be fine-grained, of 
smooth, even texture, and should have a low shrinkage and good 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, roof¬ 
ing tile, and terra-cotta. 
Terra-Cotta Clays —Clays for this purpose should be semi-refrac¬ 
tory, of fair plasticity, high transverse strength, high bonding power. 
