PREHISTORIC POTTERY PIGMENTS IN T H E SOUTHWEST
BY FLORENCE M. HAWLEY
N T H E prehistoric days of the Southwest, the people fashioned their household articles after patterns handed down from generation to generation; in fact, so conservative were they
that each of their different schools of art extended over a com- paratively large area. As in historic art, there were developments and changes in each school; these came through the new ideas of some master potter or simply through natural organic growth and decay. When the archaeologist digs up a piece of pottery, his first effort is to classify i t according to culture area, then to place itin its chronological sequence. It has long been realized that movements and developments of peoples may well be traced through a study of their pottery; the relative chronology of pottery types and of cultures may be determined through cross finds of whole vessels or even of potsherds that have been traded out of their own areas. Hitherto, only the designs, the colors, and the pastes of pottery have been considered to any extent in this study; I would suggest that the difference in types of prehistoric paints as discovered through simple physical and chemical tests or through more complete analyses presents a field of study offering new discoveries. I t has been found that the types of paints used in a given locality were consistent and so provide a dependable basis of comparison with the paints of other wares. Up to the present time there has been little scientific investigation of these American prehistoric paints, though in 191 1 Louis Franchet printed a comprehensive study of paints and pottery other than American in Cbamique Primitive.
For the more comprehensive chemical tests the paint must be removed from the sherds in some way so that little of the sherd itself comes off with the paint. Because of the exceeding thinness
732 AMERICAN ANTHROPOLOGIST [N. S., 31,1929
of most paint coatings, such a removal is difficult, and as the simple tests were found to be practical in almost every case, the longer chemical tests need be used for only the manganese paint, for which we have found no shorter test, or as a check if the result of any simple test is doubted. Because the black paint presents a much wider range of differences than the other colors, i t has been found to be the most valuable for the study of culture areas and influences. Of the four colors commonly used in pottery decoration -red, white, buff, and black-all but the black are mineral paints. Both vegetal and mineral paints and combinations of the two were used to produce black.
Before one may make a detailed study of the paint materials, something must be understood of the process of making pottery, of the application of the paints, and of the firing. These processes noticeably afiect the colors of most of the paints used by both the modern and the ancient Pueblo Indians. That the modern process of preparing the clay probably closely parallels the ancient is indi- cated by the marked general resemblance in pastes of modern and ancient wares, although in composition the different classes of both the modern and ancient pottery may differ noticeably.
The lower part of a vessel is often molded in a pottery bowl or in a large sherd saved for the purpose, although I have seen pieces of modern Hopi ware that show the unmistakable imprint of a modern pan upon their lower portions; verily the Indian will be civilized! The bases of some pieces of prehistoric ware were molded in baskets; imprints of the rim or of a few coils are oc- casionally found three or four inches from the base of the vessel. Pottery vessels or sherds were probably used for base molds of other pieces then as now. Upon the clay base the potter builds up the rest of the piece by coiling long ropes or fillets of clay around and around upon themselves. This coiling process, used by the ancient as well as by the modern potters of the Southwest, insures a symmetry rivaling that obtained through the use of the wheel by the early potters of Europe. Hand modeling couldscarcely reach such perfection. Vessels in which the coils were not obliter- ated show that in this type, a t least, no base mold was used; the entire piece was built up by coiling.
HAWLEY] PREHISTORIC POTTERY PIGMENTS 733
The coiling leaves the surface rough; the woman smooths i t with a small paddle cut from a piece of gourd rind or with a wooden paddle that is slightly larger. I n those wares on which no slip was used, as the ancient San Juan massed black-on-white and the modern Hopi, this smoothing is prolonged until a thin emul- sion of the finest particles of clay comes to the surface and so fills in the pores that the appearance of a slip is produced. After the smoothing, the Hopi woman allows the pottery to dry some- what and then rubs i t down with a piece of white sandstone. In slipped ware, the slip is now applied and dried, and the vessel is given a final polish with a waterworn pebble; unslipped ware is similarly polished. The woman mixes her pigments in a small stone metate or in a more modern cup and applies them with home- made brushes of yucca fiber. Prehistoric artists used paint slates, tablets, or stone cups as well as metates for grinding and mixing their colors.
After the colors have dried for a few hours, and the modern Hopi finds the oven of the white mans stove most efficient for this process, a number of the completed vessels are stacked and fired in an outdoor oven of slabs of dried sheep dung; the same material was used for fuel. The cracks of the oven are filled with small pieces of the dung, so that a red heat may be obtained, a tempera- ture that will burn the pottery to almost the hardness of porce- lain. Firing lasts for only about an hour. Little of the ancient pottery was of as fine clay or as well burned as the modern Hopi ware except for that massed black-on-white ware that is charac- teristic of the San Juan and particularly of Kitsil and Betatakin ruins in the Segi canyon. Underburning gives a bad color and weakens the vessel; overburning discolors the pigments and the clay. Before the Spaniards brought sheep and cattle into this country wood and perhaps a little coal was used for fuel, and open fires or ovens of stone slabs leaned together must have been used.
YELLOW, RED, AND WHITE PIGMENTS The firing changes the colors of many of the pigments and
makes them permanent. The white clay that the Hopi use for the walls of their pottery turns to cream or even to buff in firing and
734 AMERICAN ANTHROPOLOGIST [N. S., 31,1929
may become orange if overfired. This is due to a slight content of yellow iron oxide in the clay. The yellow ochre, limonite, (2Fez032Hz0), is ground and used for the walls of their red ware and for any red designs on the light ware; upon firing, the yellow iron oxide changes to red iron oxide, (2Fe2O3), with a deep brownish red color. The modern Hopi do not slip their vessels; the high polish produced by patient rubbing with a smooth pebble produces a background which so simulates a slip that i t is usually mistaken for one. The same yellow clay was used for the slip of the Little Colorado black-on-red ware, and in a less pure form and color, for the exterior of the Middle Gila polychrome vessels and for the great amount of undecorated red ware found all through the Southwest. Guthe reports that the orange-red slip used on the bases and on the interior of olla lips a t New Mexico pueblos is of a mustard yellow shade until fired. This yellow iron oxide burns to a lighter red than that used by the Hopi, and unlike the Hopi, these people use a red iron oxide wash for their dark red slipped decorated ware. Equal amounts of rock temper and white clay are mixed with water and are made into cakes which are dried and stored away. When needed for use, these cakes are broken up and enough is put into water to give i t a milky opaque appearance. To this is added an indefinite amount of the red clay, the amount depending upon the shade desired. Stevenson, speaking of the Zuiii, wrote, The materials used to produce the red or brown colors is a yellowish impure clay, colored from oxide of iron; indeed it is mainly clay, but contains some sand and a very small amount of carbonate of lime [It] is generally found in a hard, stony condition and is ground in a small stone mor ta r . . . . and is mixed with water so a s to form a thin solution.
The Hopi claim to use no red clays or pigments except for body paints. Oval pats of clay mixed with ground hematite to produce a deep red body paint were found in Turkey Hill ruin, near Flagstaff. The clay was added to give thickness to the paint. These pats had been bored with a transverse hole so that a string might be run through them for suspension.
Dead white or grayish white clays were used for the white paint, and, containing no oxide of iron, did not change color in firing. Stevenson found inodern Pueblo Indians using
HAWLEY] PREHISTORIC POTTERY PIGMENTS 73 5
a fine white calcareous earth, consisting mainly of ground feldspar with a small proportion of mica.
The material used for white paints may have varied somewhat among the tribes but must always have been some mineral free from iron oxides. Kaolin clay was probably the most com- monly used.
Black paints have hitherto been the subject of some conjecture. Carbon paints containing no silica would immediately burn off; graphite is much too rare for general use as a paint. The balls of carbon which are occasionally found in ruins were intended for body decoration and not for pottery; such material could not have been made permanently adherent.
In 1903 Hough spoke of the black paint of the Little Colorado region- the basis of which is iron ore, but the secret of its mixing, whether with alkaline salts or resin, is lost, . . . .
The present study of black paints, which has thrown some light upon that secret, has been carried on through chemical tests made of the prehistoric paints. The data so secured were corre- lated with those from similar tests of modern Pueblo pottery paints. The results indicated that in their pottery decoration, as in many other fields, these descendants of the prehistoric peoples have carried on the traditions and customs of their ancestors and that an examination of the materials and of the preparation of the modern paints might be expected to furnish those con- necting links of fact that are not apparent in a deductive study. The apparent constancy of a paint type in an area in one or more periods led to an investigation of the relationships between culture areas as indicated by the change in paint areas in different periods.
TYPES AND TESTS OF BLACK PIGMENTS On the basis of tests made the black paints used on prehistoric
1. Plain carbon similar to soot or lamp black, applied by smudging.
2. Carbon protected by a thin, adherent, transparent film of an easily
pottery may be divided into four main classes:
(Not a true paint.)
fusible silicate. This is the vegetal extract paint.
136 AMERICAN ANTHROPOLOGIST IN. s.,31,1929
3. Carbon protected by the silicate, with the addition of red iron oxide (Fe20s), or yellow iron oxide) 2FeZOs2Hz0), which burns to FezOs.
4. Paint containing chiefly some manganese oxide, (MnOJ, (Mn,04), or (MnOOH).
T y p e 1. Smudge.--For some years i t was thought that those vessels showing a satiny black interior had been treated with a glaze paint and that those with rough, dull black interiors had been covered with dull paint. Test 1 indicates that these pieces were smudged black by the same method as that used by the women of San Ildefonso. After the vessel is fired it is filled with smoldering organic material and kept warm upon the coals. This treatment deposited carbon around the particles of clay of the slip or of the polished surface where there was no slip. In some cases the darkened film of clay is thin; with longer subjection to the smolder- ing matter, carbon was driven halfway through, or, rarely, entirely through the walls of the vessel. The dull or shiny appearance of the finished surface is due to the relative amounts of polishing the surface receives before firing.
Cushing describes a slightly different process which would produce the same smudged effect. Vessels while still hot from a preliminary burning, if coated externally with the mucilaginous juice of green cactus, internally with pinon gum or pitch, and fired a second or even a third time with resinous wood-fuel, are rendered absolutely fire-proof, semi-glazed with a black gloss inside, and wonderfully durable.
The gum and juice when heated in a slow fire would deposit carbon around the clay particles of the slip just as when the vessel was filled with organic material and heated.
In an open draft mufile or with an oxygen torch, heat the sherd to redness and maintain that approximate temperature for two or three minutes. If the torch is used, the flame must be moved over the sherd so that plenty of oxygen may reach the surface. Carbon deposited by smudging will burn out, leaving the clay its original color. The depth to which the carbon has penetrated will determine the length of time i t will require for burning out.
Paint which is purely vegetal in composition and which has not burned onto the pottery would also burn off, but such paints
HAWLEY] PREHISTORIC POTTERY PIGMENTS 13 1
are very rare, the black paint used by the modern Pima and Papago being the only type I have found to burn off, and some of these people claim that they use the commercial paint. Differ- entiation between paints and smudges in such cases is not difficult. Smudges can only be applied in large undefined areas or over an entire surface; only paints may be applied in areas decorated with designs. An examination of a cross-section of the wall of the vessel will indicate whether smudge, which penetrates the wall, or paint, which scarcely sinks into the surface has been used. I n testing, the temperature to which a sherd is subjected must not be high enough for the surface to become fused.
If the black paint gives no reaction to test 1, i t should be tested for type 2 or 3 paint.
Types 2 and 3 (Carbon: Carbon and Iron).-The carbon paint of type 2 was applied as a vegetal extract. Type 3 consisted of a similar solution, to which was added iron oxide. In both types the carbon was protected by a silica film or incipient glaze.
The silica film of these types of paint must not be confused with any heavy glaze which covers the surface of a pigment. It is rather a very thin coating which surrounds individual particles or groups of particles of carbon and which, in testing, must be removed by treatment with hydrofluoric acid before the carbon may be burned out. This film protected their paint during firing. Occasionally a white crystallization of the glaze material may be seen along the edges of...