CLAYS OF NEW TOEK 



651 



enamel, and a glaze whicli shall be free from cracks or crazes; tlie 

 latter are due to the body and the glaze having a different coefficient 

 of expansion. 



Enamel brick are made of twO' different sizes, known as the 

 English and the American size, the former being 9x4|^x3, the 

 latter 8fx4|x2f . 



Many manufacturers are able to produce a wide range of colors; 

 the number is constantly being added to. Owing to the ex- 

 pense of manufacture, the cost of these bricks is usually high, and 

 varies from $60 to $90a thousand. 



The body of the brick is usually made of several different clays, 

 and much depends on the selection of the proper material. On 

 this mixture the method of burning sometimes also depends. 



The clays used for the body of the brick are molded either by the 

 soft mud, dry press, or stiff mud process. The glaze is sometimes 

 applied to green bricks before being burned; or at other times the 

 brick is first fired, the glaze then applied, and the twO' subjected to 

 a second burning, which is at a lower temperature than the first. 

 The one is known as the single fire process, the other as the double 

 fire process. 



Enamel bricks are usually made with an indentation on the upper 

 and lower faces. In laying a wall the mortar is put in this space, in 

 such quantity that when the bricks are pressed together a thin 

 layer of it is forced out toward the edges and furnishes sufficient 

 binding material. This does away with " pointing " at the joints,, 

 and a wall properly laid should show almost no mortar between 

 the courses. In consequence of this mode of laying, every brick 

 should be true to the standard size in order tO' secure a regular and 

 perfect bond. It is, therefore, necessary to know the exact shrink- 

 age that occurs in burning, and to allow for it by giving to the 

 dies used in pressing the brick the proper amount of " over size." 



In a good enamel brick the enamel should adhere so tenaciously 

 to the body that it will not separate or crack under pressure till the 

 body of the brick fails. 



