An equally disagreeable task is the sounding which the "cuiseur " must make every morning to test the degree of baking of the bricks placed the day before. If he finds them too much baked he will consequently diminish the coal; he will increase it, on the contrary, if the firing has not been active enough.
Sometimes several clamps are made "a blanc," that is to say, without coal; this is done when the fire is too violent, or when a change is made from a more to a less strong clay. The number of clamps that can be stacked in a day depends upon the conduct of the fire. If it is active and uniform, seven or eight or even ten may be erected, but if it is not active, we must be careful not to build too many, for the fire would slacken and smoulder, which exposes the bricks to the danger of being burnt by sudden bursts of flame. When, at any point, the fire rises less quickly, its progress is assisted by making one or two less clamps and thus leaving a vacant space which is filled up on the following day.
At the beginning of the days work, no smoke appears, because poor coal is used; but at the end, the water from the bricks evaporating forms white vapour, which, if the weather is damp, become so compact sometimes that all work is rendered impossible.
The skill of the "enfourneur" consists in being able to make the facings of the clamp perfectly perpendicular, and especially in placing properly the bricks at the edge, for the clamp rises to six or even seven metres in height, and not only must it resist the pressure of the load, but also that of the tire. This is because the centre, being always more baked than the edges, undergoes less contraction; also, towards the edges, the combustion of the coal is less complete than in the middle, and the effect of all these causes is that the subsidence is more marked here than in the facing. This inconvenience must then be remedied.
Fig. 201. Brick Barrow (Whittaker).
To raise the bricks on to the clamp, special wooden or iron barrows called "brouettes a barque" are used.
The clamp is ascended by means of inclined planes formed of planks resting on trestles, which are raised every day; a second but steeper plane is used for bringing down the empty barrows. Planks are also placed on the bricks for the barrows to run on, and are taken away in the evening. When the clamp has reached the required height, it is covered with a bed of clay which will become baked while preventing the heat from leaving the upper layers too soon. This clay, when crushed and passed through a sieve, will be used by the moulders for powdering their moulds.
When the weather is fine, the brick dry, and the stoker skilful, there are no accidents; but the inclemencies of the weather, rain, wind, etc., have to be considered.
To guard against the wind, screens are constructed with poles and straw matting, but this does not prevent the gusts of wind which pass over the top and drive back the flame. The latter concentrates and endeavours to escape, thus causing inflation of certain parts of the facing. The furnaces must be at once opened, and if that is not enough, the clay coating must be at once torn down in order to avoid a breach likely to cause serious accidents which would damage the firing and might even ruin the whole mass.
As for rain, it is difficult to avoid its bad effects; if it threatens in the evening, sand and coal are added to protect the surface of the bricks. If it falls when the fire is near the surface, no great harm is done. But if it comes on towards the end of the day, that is to say, when the fire is at some distance, it may cause, according to its violence, the loss of one or two clamps, which will then have to be removed, sometimes with shovels if the bricks are softened.