Tile-kiln.
A form of kiln adapted to
burning tiles.
A good form of tile-kiln, as used in
Staffordshire, England, is shown in the accompanying figure.
On the bottom of the oven are first placed 2,000 bricks, as shown at
a, which is a plan of the oven as seen when eight courses of brick are laid edgewise.
The eight rows, with twelve bricks in each, as seen in the plan, cover a space left in continuation of flues from the eight fireholes.
The bricks in the first seven courses are so placed as to leave a flue of an average width of 4 inches. The dotted lines show the position of the fire-holes.
Upon these bricks are placed 7,000 tiles, forming a square, the spaces between the tiles and the curved sides of the oven being filled up with bricks, as seen in the figure.
b is a plan of the oven as seen when the first course of tiles are placed upon the bricks, seen in the figure
a. The tiles are placed in bunches of twelve, and laid alternately cross and lengthwise; the nib on each tile spaces it from its neighbor and supports it in vertical position.
The spacing of the bricks and tiles allows the circulation of the heat between them, and the circular oven is found well adapted to secure uniformity of heat.
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Tile-kiln.
A, plan of brick courses.
B, plan of tile courses. |
The kiln is protected on the windward side, to prevent uneven urging of the tires.
The oven being
set, the doorway is bricked up and daubed, the fires kindled and kept burning, moderately at first, and then more freely.
The usual time for firing is thirty-eight hours, and the consumption four tons of coal for a kiln of the size described.
Three days are then allowed for cooling and they are afterward taken out of the kiln.
Those tiles which are to be made of a grayish color are thus treated.
It having been ascertained that the tiles are burnt enough, and while still red-hot, a quantity of small tagots of green alder with the leaves on is introduced into each flue.
The flue-holes are then well secured, and the holes in the roof each stopped with a paving tile and the whole surface is covered with four or five inches of sand, on which a quantity of water is thrown, to prevent the smoke from escaping anywhere.
It is this smoke which gives the gray color to the tiles, both internally and externally.
The kiln is then left closed for a week, when the sand is taken off the top, the door and roofholes are opened, as also the flue-holes, and the charcoal produced by the fagots taken out. Forty-eight hours after, the kiln is cool enough to allow of the tiles being taken out, and the kiln charged again.
Whenever any of the tiles are to be glazed, they are varnished after they are
baked; the glaze being put on, the tiles are put in a potter's oven till the composition begins to run The glaze is generally made from what are called lead ashes, being lead melted and stirred with a ladle till it is reduced to ashes or dross, which is then sifted, and the refuse ground on a stone and resifted.
This is mixed with pounded calcined flints.
A glaze of manganese is also sometimes employed, which gives a smoke-brown color.
Iron filings produce black; copper slag, green; smalt, blue.
The tile being wetted, the compositon is laid on from a sieve.
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Hunt's tile-machine. |
