account. Pyrometers are also used, but with all these aids the experienced fireman pays due regard to sight and colour.
For a craftsman, the kilns that have been described are unsuitable on account of their size, if they are not altogether beyond his means. But a kiln of some sort is indispensable to a potter. The craftsman is nothing if not inventive. Small trials can be fired in crucibles in an open fire or on a gas ring. I have heard of some preliminary success with a gas cooker, discounted later by a frontal attack from the cook. Considerable knowledge can be gained from small, easily constructed, experimental kilns.
The small trial kiln shown (Fig. 70) was constructed with a stout old crock, over which was built a core of bricks plastered with marl. The fire was started at each corner at the bottom, and when well alight, fed from the top with coke. A small spy at one corner closed with a piece of biscuit gave some idea of the progress of the firing. This, of course, had to be practically rebuilt at each firing, but as a makeshift was quite satisfactory.
Fig. 70
Fig. 70a
The gas and oil kilns described in Chapter IX are excellent as far as they go, and indeed the only practicable kind for indoor schools. But their restricted size soon becomes irksome to a craftsman, whilst the expense of firing makes only the finest work remunerative. For over-glaze work they are excellent, but for some reason glazes fired in them seem to lack some of the richness and maturity the same glazes exhibit when fired in the slower and more soaking fire of a brick kiln. The dug-out kiln here depicted (Fig. 71) would be quite suitable for summer schools or for a craftsman making soft peasant pottery. The section and sketch will indicate its construction. The materials are hard bricks and stout old boiler plates, or sheet iron. To pack or unpack, the middle section of the roof would have to be removed each time, and all glazed pots would need protection from scalings and gravel from above. The roof will sag at any big heat, and if of thin iron, will need propping. The firing would be done with soft coal or wood; a very slow start, with a brisk draught and a long flame at the finish.
Fig. 71