Kilns
“By many long, laborious, and chargeable experiments he hath found out.”
—Extract from an old potter’s patent.
What must be the first representation of a kill, or kiln, is found at Beni Hassan. It appears to be square in form, and the potter is shown feeding the fire at the base. In the same illustration he is depicted unpacking or drawing the ware from the top. The cut from the Greek Hydra gives a very
similar kiln, but a vessel in the museum of Berlin shows one with a beehive shape.
The kilns left scattered about Europe by the Romans were usually of this domed kind, circular in plan, with one fire hole. The floor of the kiln was of pierced slabs, and the flames issuing thence enveloped the ware piled within and escaped through a vent in the top. The packing and firing is described in Ceramic Art in Great Britain, by L. Jewitt, F.S.A. It fully explains the trepidation of the old potters, who, before each firing, were wont to consult the moon and stars and evoke the aid of the gods. This is happily set forth in Cowper’s translation of one of Homer’s epigrams, wherein he expresses the pious hope that if the false potter “stoops to peep into his furnace, may the fire flash in his face and scorch it”; a risk often faced by potters, false or true!
The smothering, or reducing, as then practised, was similar to the lustring methods used in Italy in the sixteenth century, or in the manufacture of the blue bricks to-day. The Japanese and Chinese built small kilns in tiers on the side of a hill. Starting with the lowest, the waste heat was utilized to warm up the kiln above, thus saving time and fuel. The Chinese used heavy saggars, and specimens of these with portions of melted pots still adhering to them attest the enormous heats to which they frequently attained.
Modern kilns subdivide roughly into biscuit, glost, and enamel. The first is used for firing the green or clay shapes, the second for the hard fire of the glazed ware, and the last-named for fixing on the added decoration. Sometimes a kiln is used for the double function of biscuiting and glazing.
Of modern kilns the one still most widely used approximates to the bottle-shaped, simple, up-draught kiln. It contains one or two chambers with hatch for entry, flue or chimney, and anything from three to nine fire holes. The section of such a kiln is here shown and represents a fair average up-draught kiln (Fig. 66), variants of which type are working in most pottery districts to-day. In these kilns the flames rush in at the fire holes, play on the built-up bungs of saggars, and escape through the top vent. In a two chamber kiln, as sometimes used for porcelain, the glaze is put in the lower chamber to receive the hottest fire, the biscuit in the upper getting a gentle fire. Where the fire enters directly into the kiln in any large volume, bags or small chimneys are built up inside the mouths to save the saggars from the worst of the fire. Of late the single-chamber, down-draught kiln has come into favour, as it is easily packed and economical of heat. Bags of firebrick protect the saggars from the roughest fire and direct the flames to the crown of the chamber, from which point they descend to pass out through flues in the
floor of the kiln. (Fig. 67.) Biscuit ovens are often of this type, either domed or flat arched.