This is the final drying, and they are then carried to the oven twelve at a time, with the edges of the tiles resting against the breast of the carrier.
Objections to roofing tile, in this country, have heretofore been made to the effect that the tile was heavy, made of coarse clay, poorly burned, that it would absorb a great amount of moisture, so that freezing and thawing would cause it to crumble, and, in appearance, it was anything but handsome. Whatever foundation these objections may have had in the first product of tiles, our manufacturers have now fully met and remedied these drawbacks to their use.
All roof-tiles require more careful burning than brick, and before they are placed in the oven, the bottom is covered with brick, so as to take the first flash of the fire, which would de stroy a course of tiles in that position from the warping and discoloring.
On the top of this course of brick about nine thousand tiles are set, which form a square in the heart of the kiln, the space between the tiles and the curved sides of the oven being usually filled with brick.
The tiles are set edgewise in lots of twelve, called bungs, changing their direction with each lot, being set cross and lengthwise alternately. They are placed in a vertical position, and the nibs of the tiles space them off from each other and support them in a vertical position ; the checkered manner in which they are placed in the oven insuring full action of the fire through the stock.
A uniformity of heat is a great desideratum in burning tiles, and the old form of circular oven, so much employed in Staf fordshire, is found to answer the purpose, and do the work more thoroughly than any other in use.
A wall is sometimes built around the oven in order to pro tect the fires, and prevent one from being urged more than another by the changing direction of the wind.
A sufficient space is left between the wall and the oven to allow the fireman to attend conveniently to his fires ; five feet six inches usually being high enough for this wall.
The oven having been filled, the doorway is walled up with brick and faithfully daubed over with loam and sand, the fires are lighted and kept slowly burning for the first five hours, after which time they are then progressively increased for the next thirty-three hours, making the total time thirty-eight hours for hard-fired tiles, four tons of coal being consumed in the burning. The fireman determines the heat by directing his sight to the mouths and top outlet of the oven ; when the heat is reached, and before the fires burn hollow, the mouths are stopped up with ashes to prevent the cold air from cooling the oven too quickly.
The ovens are fired once a week, but can be fired easily three times in two weeks if so desired.
The manufacture of plain roofing-tiles can be conducted with a small capital, the process and requirements not being very in tricate or expensive.
But to conduct the manufacture of all the tiles required for roofing, and the other articles generally produced in large tileries, requires a large capital and a thorough knowledge of the business in all its details. -