Raised designs are also produced by pressing out the wall of the pot from within. Another method, of restricted distribution, is that of scraping away the surface so as to leave the figures in relief. This is found on some of the pottery from parts of New Guinea.
The colour of a vessel is to a great extent dependent upon the composition of the body and the method of firing. Of materials present in bodies iron is usually the only colouring element. This on being subjected to heat under oxidizing conditions is changed into a red iron oxide and gives a shade varying from yellow to an orange or red. Under reducing conditions, that is if the atmos phere contains little or no oxygen and an excess of hydrogen or carbonic oxide, the chemical change is different, producing a colour ranging from light bluish grey to a deep, sometimes metallic, black. Usually among primitive peoples no effort is made to pro duce certain shades by regulating the conditions of the firing, the method used to produce the colour combinations of the famous black-topped ware of pre-dynastic Egypt. A dark colour is often the result of a pot's being smoked; this may be an un intentional incident of the firing, but among the Ashanti it is brought about by setting the vessel, while still red-hot from the furnace, on a heap of dry tinder. This it ignites. Water is then poured on and the pile is left smoking. The smoke permeates the heated clay and deposits on and sometimes through it a mixture of finely divided tar and carbon, rendering it non-pQrous.
Decoration by means of slip is occasionally found, but true painted pottery is extremely rare among backward peoples. The Ba-Thonga produce a bright brown colour from a decoction of boiled bark, and among the Banyoro of East Africa vessels made exclusively for the king are covered with a mixture of powdered graphite, water and the glutinous juice of a shrub. (This should perhaps be regarded as a varnish rather than a paint.) A process of staining is performed by the Nicobar islanders. While the pot is still hot, strips of unripe coconut husk are laid on it and the acid juice makes a black mark. The pot is then further rubbed over within and without with these same strips moistened, which gives to the unblackened parts a light copper colour. At Port Moresby (New Guinea) chewed mangrove root is used for the same purpose.
Varnishing.—Fired pots will not absorb water, but are nearly always porous and sweat. They are therefore frequently var nished and this varnish is often decorative as well as useful. Many different methods are employed. In Fiji and Borneo the clay while still hot is rubbed over with pine resin and in Central Africa with gum copal ; in southern Nigeria the ware is boiled in palm oil, and in Huon Gulf (Mandated New Guinea) it is washed over on the inside with a mixture of sago and hot water. Among the Pueblo of North America the juice of a green cactus is applied externally and piiion juice or pitch is smeared inside, after which the pot is re-fired; while farther north, in the area of the Great Lakes and among the Eskimo, the pots are rubbed over with grease and coated with a solution of boiled maize.
Similar in artistic effect to varnishing but without so great utilitarian value is the practice of polishing or burnishing the ware, but this is only possible where the clay is of a fine body.
Though vessels are the most common pottery products of primi tive peoples other things are sometimes made. Tobacco pipes (q.v.) of elaborate shapes and fine workmanship are found in Africa, and pottery drums made in the shape of large water jars. Among the Ba-Thonga and Akikuyu children are adept at making toys and models which are sun-baked, and in southern Nigeria these are made by men and women by plastering the clay over a frame-work of corn stalks, by which means remarkably life like figurines are produced.
Sociological and Religious Aspect.—Little attention has as yet been paid by ethnologists to the religious and sociological as pects of pot-making. Generally the craft is confined to one sex, usually the female, except where the potter's wheel is used, which is always operated by men. In so far as domestic utensils are naturally matters which concern women it is not strange that they should be the potters, but this does not explain why, in many cases, men are definitely prohibited from potting nor why their very presence during the manufacture is inimical to it. Thus among the Sema Nagas of Assam a man may not even speak to a woman thus engaged nor approach her work. Such prohibitions are but part of the means by which success in the work is ensured. Pottery is liable to accidents which are beyond the control of the worker : however great the care taken many pots become cracked and distorted in the firing. Therefore tabus are instituted to guard against such mishaps. What cannot be controlled on the natural must be controlled on the supernatural plane. For this reason the Ashanti will not allow an unbaked pot to leave the village nor count them before firing; among the Ba-Thonga a child must light the pyre and the clay when being seasoned must be placed where none will walk over it. Occasionally certain tabus apply to certain varieties of wares. Among the Ba-Ila only men may make pipes, and among the Ashanti no woman may con struct a pot of human or animal design lest she become sterile. The making of ceramics is often the prerogative of certain families or a certain district and any infringement of this may easily cause trouble. Even where this is not so, certain villages become famous for their wares. It is said in a part of British New Guinea that a native can tell from the appearance of a vessel where it was made and even the woman who made it. Trade-marks are sometimes used. In the Nicobars each maker has her own peculiar device which she incises upon her products before firing. Care is taken not to infringe upon the rights of another nor to adopt a design which may be mistaken for one already in use. Trade-marks are also recorded from Port Moresby (New Guinea) where the women produce wares for an important trade with tribes living farther up the coast.
Considering the many different techniques it is commonly held that pottery was invented independently in many parts of the world. From the practice in America of making vessels by lining basketry moulds with clay it has been surmised that at first baskets were thus lined to render them non-porous and then, when by accident such a basket was destroyed by fire, the resultant clay vessel suggested the making of pottery. The coiling technique of America, too, seems to be closely allied to the coiled basketry of that region. Theories of origins are necessarily speculative but in evolving them it must not be forgotten that, as any one who has made pottery will testify, clay shaped and burnt does not produce a pot. The body must be properly prepared, the vessel properly dried and fired under suitable conditions. The accidental discovery of pottery, therefore, is not so easy as has sometimes been implied.