Ten or fifteen minutes after the smothering the first piece is dug out of the mound with the poker. It is placed a foot or two from the oven and hastily wiped with a dry cloth to remove all manure. The surface of the vessel is a beautiful shiny black color, which does not change at all on cooling. If black ware paint (see p. 24) has been used, it changes from the greenish-yellow color that it had before burning to a dead matte black which contrasts very effectively with the polished surface of the vessel (see [pl. 8], a). At first the vessels come from the smoking mound slowly, and all holes left in the pile by the removal of vessels are carefully filled again, but later they are taken out as quickly as possible, and toward the end no attempt is made to keep the pieces still in the pile thoroughly covered. If, when a vessel is removed, its condition does not quite suit the potter, it is replaced in the smoking manure and completely covered.
Certain polished black vessels are further manipulated in such a way as to produce an irregular red blotch upon them.[50] Specimens destined to receive this red blotch, which is usually placed near the rim, are reburied in the hot manure lying round the edge of the pile with that portion which is to have the blotch left uncovered. Against this exposed portion is placed a smoking fragment of a dung-slab. The action of the heat and air results in the removal of the carbon from the surface, so that that part of the vessel which is not covered with manure and ashes regains its former color, the red of the pigment. Since the pot is pushed about a good deal during this process, the line between the red and the black surface is not always very definite, which improves the appearance. The Indians themselves cannot tell beforehand just what shape the blotch is going to take, and must therefore watch the vessel continually. Sometimes burning shreds of cedar bark are placed against the exposed surface to hasten the process, but actual flames are not necessary in order to obtain the desired result. If the red blotch is too large, part of it is simply recovered with hot manure-ashes, and a few minutes later will again become jet black. So far as looks are concerned the success or failure of this red blotch upon black ware depends largely upon the artistic sense of the potter making it. In one group of thirty-three polished black vessels fired together, sixteen were given a red blotch; eight or ten of these were excellent pieces.
The time consumed in burning polished black ware is shown in Table XI. It should be noted that before the loose manure was added, the vessels were subjected to the fire about the same length of time as those of other wares.
TABLE XI
| Minutes | |||
| Preparation and building of oven begun | 00 | 00 | |
| Fire started | 16 | 18 | |
| More fuel added | 41 | 39 | |
| Oven smothered with loose manure | 46 | 45 | |
| First bowl removed | 59 | 59 | |
| Last bowl removed | 74 | 99 | |
Accidents
The accidents which may occur in firing are of two general classes—those which result from faulty treatment during the construction of the vessel itself and those which are due to careless manipulation in burning. The latter are the more frequent.
A vessel may crack or flake badly in the oven; often the entire base breaks off. The fault in this case lies in the original moulding, because small stone fragments or air-bubbles were allowed to remain embedded in the paste. Since the rate of expansion under heat varies for different substances, a great strain develops about such stones or air-bubbles during firing, and the natural result is cracking or flaking of the clay. In some larger vessels the slip flakes away around the shoulder, where the two areas of the surface met when the polishing was done (see p. 64). In the potter’s opinion these flakes, which are exceedingly small, are probably caused by minute air-bubbles that had lodged under the slip while the line about the shoulder was being polished. A third type of accident is merely a blemish; it is due to flies settling on a vessel before burning; the resulting fly-specks are burned into the clay, and the surface of the pot is sprinkled with dots quite as black as guaco decorations.
The most common form of blemish caused by careless manipulation during firing is the “smoke-cloud” or “fire-cloud”, a circular blackened area, the darkest part of which is at the centre. There is no question but that this is caused by contact between the vessel and a dung-cake, and the result is probably due to moisture in the dung which brings about a deposit of carbon on the surface. If, during the burning, a cake of dung falls, it will probably come in contact with the surface of some bowl. If it is removed at once there is little danger of a smoke-cloud, and the potter, when she notices such an accident, immediately tries to secure the fallen cake with two pokers. With much skill she carefully extricates it from within the oven without disturbing the other cakes about the place from which it fell. Fire-clouds may be produced upon the bases of vessels by setting them on hot cakes of dung before firing; or upon damp, or relatively damp, ground immediately after firing. Excessive dampness, such as steam from wet ground under the oven, may in addition to discoloration, produce warping of the vessels. Another sort of blemish is occasionally caused by rust from a tin can resting upon a vessel during firing; such a spot is usually reddish brown in color, and covers a very small area.