636 NEW YORK STATE MUSEUM 



USES OF CLAY 

 Characters of brick clays 



Under this head is included a very wide range of materials, de- 

 pending on the quality of the product to be made. 



For common building brick almost any clay of good plasticity 

 will do, and this very fact has been most extensively abused by 

 brick manufacturers, encouraged by indifference on the part of con- 

 tractors who are very often inclined to regard common brick as 

 simply so many cubic feet of burned clay, little attention being 

 paid to the quality of the product. 



As the different kinds of brick can not all be made from the 

 same kind of clay, it will be best to consider separately the requisites 

 of the clays used for these different types. 



Clays for common bricks. For this purpose the more impure clays 

 are generally utilized, and in general those which bum to a red 

 color. Calcareous clays are often employed, specially around Chi- 

 cago. Such clays produce a buff product. Many morainic claya 

 of south central New York are of this nature. 



Clays for making common brick should burn to a good red color 

 at a temperature not greater than 2000° F. or 2100° F. They 

 should also have sufficient fluxes to cement the clay particles to- 

 gether, forming a hard dense body, when subjected to the above 

 amount of heat. From 5^ to 7;^ of iron is desirable, as this amount 

 has been found to exert the best coloring action. A large amount 

 of lime is undesirable, for it brings the temperatures of fusion and 

 incipient vitrification too close together, though with care a good 

 brick can be made from a clay containing 20^ to 25^ of carbonate 

 of lime. (Seger's Ges. Schrift. p. 265) The celebrated Mil- 

 waukee brick contain 22;^ of lime carbonate and the clays used for 

 making front brick at Canandaigua, IST. Y., have 20^-23;^. 



The tendency of lime as previously stated is to lessen the shrink- 



