These terms are used to designate bricks that have a glazed surface, the term "enameled'" being applied indiscriminately to all bricks having such a surface.
There is, however, quite a difference between a glazed brick and an enameled brick. The true enamel is fused into the clay without an intermediate coating, and the enamel is opaque in itself, whereas a glaze is produced by first covering the clay with a "slip" and then with a second coat of transparent glaze resembling glass.
In the manufacture of glazed bricks the unburnt brick is first coated on the side which is to be glazed with a thin layer of "slip," which is a composition of ball clay, kaolin, flint and feldspar. The slip adheres to and covers the clay, and at the same time receives and holds the glaze. The glaze is put on very thin, and is composed of materials which fuse at about the temperature required to melt cast iron, and leaves a transparent body covering the white slip. With a glazed brick it is the slip that gives the color of the brick, and as the slip covers the brick, the latter may be either red or white. Not all bricks, however, are suitable for glazing.
Enameled bricks are made from a particular quality of clay, generally containing a considerable proportion of fire clay. The enamel may either be applied to the unburnt brick or to the brick after it is "burnt. The latter method, it is claimed, produces the most perfect brick.
In burning, the enamel fuses and unites with the body of the brick, but does not become transparent, and therefore shows its own color.
The manufacture of a true enameled brick is a much more expensive operation than that of making a glazed brick, besides being a very difficult operation. For this reason the glazed process is the one most generally employed, both in this country and in England.
It is claimed that an enameled brick is more durable than a glazed brick and will not so readily chip or peel. The enamel is also the purest white.
An enameled surface may be distinguished from one that is simply glazed by chipping off a piece of the brick. The glazed brick will show the layer of slip between the brick and the glaze, while an •enameled brick will show no line of demarkation between the body of the brick and the enamel.
After the brick are in the wall none but an expert can distinguish between the two. Probably most of the so-called enameled bricks that have been used in this country are really glazed.
The bricks are, of course, enameled or glazed only on one face, or on one face and one end. The color is generally white, although light blue and some other colors can be obtained.
Until within a very few years nearly all the glazed bricks used in this country were imported from England, but there are now some eight or more factories in this country making them, and they produce more than half the glazed bricks now used in the United States.
Enameled bricks generally differ in size from the ordinary bricks. The size of the English brick is 3 inches by 9 inches by 4½ inches. Part of the American factories adhere to the English size, while others make the regular American size.
The market price in Chicago for American and English glazed and enameled brick at the present time is $120 to $125 per M. for English brick and $90 to $110 for American brick.
The American glazed bricks are now more nearly perfect than when first put on the market, and appear to be giving satisfaction.
The true enameled brick is just as good for external as for interior use. It will stand the most severe and climatic changes, and may be used in any climate and any situation. It is also fireproof.
Both glazed and enameled bricks reflect light, acquire no odor, are impervious to moisture and form a finished and highly ornamental surface.
Use. - Glazed bricks, on account of the above properties, are very desirable for facing the walls of interior courts, elevator shafts, toilet rooms, etc., and especially for use in hospitals. They may also be used with good effect in public waiting rooms, corridors, markets, grocery and butter stores, and wherever a clean, light and non-absorbent surface is desired, and also one that will stand drenching with water.