The glaze is invariably put on after the ware is thoroughly dry. It is usually put on with a brush, but some manufacturers prefer to pour it on. This requires considerable experience and skill in order to obtain smooth results.

The preparation of slip and glaze is accomplished in the same manner as for glazed brick.

The following receipts will be found to give good results when the clay is suited to them. The rules regulating the adjustment of slips and glazes to body are the same as for brick.

Slip, No. 1—

 

No. 4 English Ball Clay..........

5

Flint ............................

48

Felspar ..............................

10

English China Clay, No. 7........

30

Plaster of Paris ...............................

7

 

100

The No. 4 English Ball Clay can be obtained from George Knowles & Son, Trenton, N. J.

Slip, No. 2—

 

English Ball Clay, No. 4..........

4

English China Clay, No. 7 ...............

40

Flint ................................

44

Felspar .............................

12

 

100

Glaze, No. 1—

 

Felspar ...........................

62

Flint ..............................

11

Paris White ..................

12

Frit, 1/2 and 1/2 Felspar and Borax..

11

China Clay .................................

4

 

100

Glaze, No. 2. Frit -

 

Borax ......

   

......26.88

Paris White.

   

......17.78

Flint .......

   

...... 17.78

China Clay..

   

...... 17.78

Felspar .....

   

...... 19.78

       
 

100.00

Glaze -

 

Take of above Frit .....................

........ 15

Paris White..............

........ 11

Felspar ..................

........ 48

Flint.....................

........21

China Clay...............

........ 5

 

100

The burning is done in muffled kilns usually. No special cautions need be given in regard to the setting of the smaller ware. Bathtubs should be set on end in sand, or, if the end cracks when set in this way, set them on bats of clay in sand. If the tubs have been dried on a clay bat, the same bat will do to set them on; if not, bats should be made specially for this purpose. The heat should be raised gradually and steadily, great care being taken, in the earlier stages, not to push the kiln. The finish must be made with great care, as overfire may warp, and underfire will not fuse the glaze. There are so many points about this business requiring special knowledge and skill that it should be entered upon very slowly and carefully, and, possibly, should not be undertaken except under the control of an expert

Qualities and Tests

The perfect enameled brick should possess a smooth, fine face, without any waviness. The face may be either bright and smooth, with high lustre, or, as some prefer, only a medium lustre and egg-shell surface. The beauty of the latter finish is that slight waves or unevenness of surface are not quite so noticeable as when the lustre is high and the polish perfect It should be absolutely certain to neither craze nor peel; it should possess considerable strength, and the different brick should be of absolutely uniform size. When we consider the different conditions under which these brick are used and the very severe treatment they sometimes get, it is not surprising that even good brick will occasionally fail by peel-ing. I have seen glazed brick piled outside buildings, without cover, fully exposed to the elements and thoroughly saturated with water before being laid in the wall; then laid in the winter months and exposed to zero weather before they had had the least opportunity to dry out. The brick stood this severe treatment, but, had they failed, the contractor should have blamed no one but himself. Such treatment of glazed brick is almost criminal, certainly outrageous. Think of the enormous strain it must be to build in a saturated brick, whose only exposed surface is impervious to water, and then freeze the water that is in the pores of the brick. We have all seen bricks that have been wet and then frozen, and we know how the expansion caused by the freezing causes a coat of ice, sometimes nearly one-eighth of an inch thick, to form on the surface. But how is the ice or water to exude from a built-in brick where even the front is not open for its passage? I do not think any maker of glazed brick should be expected to guarantee his brick against such treatment, and I think he would be perfectly excusable in refusing to do so. One might as well be expected to guarantee a boiler not to burst under a pressure way beyond what it is calculated to stand.

There is only one way of being able to make such a guarantee, and that is, in both cases, to make the article so that it will not hold any water; make the boiler solid and the brick thoroughly vitreous. Then the idiots will not be able to burst either of them. I probably write strongly on this subject, but no stronger than I feel. I have been too much worried by the treatment given to brick of my own make to write very calmly on the subject The worst part of the matter is that every fault is blamed on the brick, and no one is willing to admit that the brick may have received unfair treatment This unfair treatment is more apt to be given to American than to imported brick, because the latter are invariably shipped packed either in barrels or boxes, and are kept in the original packages until needed, while American brick are frequently shipped loose. I have seen glazed brick built in high, heavy walls, and tied to the main wall every ten courses, the joints in the glazed brick being as fine as they could be made and the joints in the common brick very coarse and heavy. This must bring an undue strain upon the enameled brick.

Testing of glazed brick is a matter about which very little seems to be known in this country. Crazing tests are easily made by subjecting the brick to alternate heat and cold, but peeling is certainly somewhat mysterious. I have seen brick fail when saturated with water and frozen that have stood perfectly in the wall, and I have seen brick stand this test perfectly that were notoriously bad for peeling when laid in the wall. Peeling from pressure is a test easily made. A good brick should not lose its enamel until at the point of failure of the brick. I do not think it quite fair to expect them to stand fully up to this point, in case it is high, but they should stand well beyond any pressure they can be subjected to in the building. If some means can be found to place a glazed brick under pressure that has been previously moistened to a reasonable extent, but not saturated, then, while still under pressure, to freeze it, I believe it would be found to be a fair peeling test. The brick should also be confined, or placed under conditions as near those that will exist when it is laid as possible.

If the brick have been made by the slip and glaze method or slip and enamel or semi-enamel methods, the slip should be well burned and should adhere perfectly to the brick body. Many brick whose slip does not seem to adhere perfectly stand well in walls, but they do not inspire the same confidence on the part of architects as hard-burned, close-adhering slips do. Color is entirely a matter of taste, but the enamel brickmaker should be able to make a perfect white, though possibly the cream white, ivory or buff may sell in preference. Colors are not often demanded in large quantities, but ability to make them is necessary, so as to be able to supply what demand there may be for them. My experience has been that the greatest demand in the color line is for brown and gray, with blue, possibly, next in order. I do not include buff as among the colors, as the demand for it seems to be nearly as great as for white, and this color must be kept constantly in stock.