Pottery, for Artists, Craftsmen & Teachers

by George James Cox

down too much, the gas lights back and will have to be turned out and relighted. The same thing happens when too much air is admitted. The burners require watching until the right pressure is known.

Fig. 47

For biscuit of any thickness three hours on the three burners is not too much, the taps being gradually turned on to increase the length of the flame until at the end of the three hours the taps are at three fourths. At the end of the first half hour the bottom spy hole is plugged and when all steam has

stopped issuing from the top vent, that is stopped also and the whole clammed, leaving just a small crack as vent. When three hours are up, the regulators are pulled back and all burners lit at half cock. Then all but 2, 5, 7, 9, and 11 are turned out. Starting at the half, they are gradually increased to three fourths in two hours. Then numbers 1, 2-4, 5-7, 8-10, 11 are lighted in the same way. Colour will begin to show inside the muffle about the fifth or sixth hour, and the top dampers can come out a little, the front one more than the back, to draw the flame towards the door.

Fig. 48

When the eight burners have been on about one and one half hours the muffle will probably show a dull red inside and all danger of blowing will be passed. Two more burners at three fourths may now be put on and at the expiration of another one and one half hours the remaining two may be turned

on. If the pressure weakens and the flame shortens, the main cock should be turned on. Just above the base of each chimney is a small hole and the flame should show through these towards the finish. If the flame flaps out of the chimney tops, it is so much waste and it should be checked at the taps. The dampers can come right out towards the end, being used to sweat the flame to the front if the back appears to come up too fast.

As white heat approaches, the cones should be observed occasionally. They turn the colour of their surroundings when about to topple over and as the first begins to curl the trial near the spy can be hooked out quickly and tested. When the right cone is well down, the main cock and then the burner taps are turned off. The air regulators are now pulled back and after a few minutes the dampers are closed. The metre is then checked and entered in the firing book.