A down-draught kiln, although more difficult to construct than an up-draught, is more economical in the end and does its work more evenly. For the benefit of those that may like to build a small and moderately cheap kiln drawings are here given. This kiln was built by me when I had very little practical experience of kilns other than gas, but it served its purpose well. It was not banded, but this is essential if the kiln is to stand hard and frequent fire. Firebricks were used for the fireholes, flues, floor, core, and dome; strong stock bricks for the rest. The glazed ware, which was fired harder than the biscuit, was saggared in bungs as usual up to about five feet; the biscuit piled on top and protected by old saggars and cracked pots from the roughest
fire. There were no bags in this kiln, but the saggars used were very strong and had stood a much greater heat than that to which they were subjected in this kiln, so that they showed very little wear or tear after twenty firings. The stack of sixteen feet gave a good sharp draught, increased if necessary by the addition of an iron chimney and regulated by an iron damper. A wind screen or hovel is advisable for rough nights, and some sort of roof is necessary to protect the crown from the weather. It is important to have the arch of the hatch very strongly built, as it has to stand a lot of strain, and an iron support
too near the fire soon corrodes and needs replacing. Another essential is that the site be as dry as possible and the foundation made solid with concrete; otherwise even a small kiln is liable to settle and crack. With a little extra expense a kiln of this kind could be banded round the impost and fireholes, thus considerably prolonging its life.
Fig. 72a
Fig. 72b
Fig. 73
In firing this kiln about half a ton of coke and three quarters of a ton of good hard coal, giving a long flame, was used. Coke for the slow fire was first started on the bottom and maintained for sixteen or eighteen hours, lifted up on to the bars for another six or eight hours, when the saggars would begin to show signs of colour. The coal fire was then started about the 24th or 25th hour and continued another 18 hours, more or less, according to the varying conditions, making in all some 40 or 45 hours. This gave a very evenly graduated heat from cone 1 at the base to cone .03 at the top. Bags were tried experimentally, but whilst giving a more uniform heat, took much longer to fire up. At the finish of the firing the fireholes were bricked up, the damper closed when the fires died down. In about 24 hours the vent and the hatch were eased a little at