This investigation of the chemical composition of the potsherds found in the Verde Valley, and of some found in the Flagstaff district was undertaken for the purpose of attempting to establish origins of certain pottery types; that is, to determine whether a certain pottery type was made in the district in which the sherd was found or whether it had been traded from some other district. Most of the work done has been on the Jeddito Black-on-Yellow or Old Hopi potsherds, as it seems to be the most commonly occurring pure paste type. Numerous sherds of other types were examined also for comparison.

The spectroscope is especially suited to the determination of elements present in small amounts, so for comparison of composition of the sherds, the elements were selected which were present in small amounts — chromium, sodium, copper, calcium and manganese. It would be possible to make the method absolutely quantitative by using the Wedge Sector method, but it would be difficult if not impossible to make exposures such that all five of the above elements could be determined in one exposure. If the determination can be narrowed down to that of one element only, the percentage of that element can be determined very closely. For the present investigation, however, a strictly comparative method was used. The largest amount of the element occurring in any of the sherds examined is designated the by the figure 10, and the smallest amount by 1 or 0 if it is entirely absent, The figures from 1 to 10 are comparative only for one element; that is, the amount of copper repesented by the figure 5 bears no known relationship to the amount of manganese which may be indicated by the same number 5.

The one content thing about the Jeddito Black-on-Yellow type is that all the sherds examined were made from clays very low in manganese. Very few sherds of other types that were examined show this characteristic. Clays from different districts in the Verde Valley have been examined and none of them could have been used in the Jeddito Black-on-Yellow. Two clays from the north have been examined also, one from Walpi, and one from Hano, and neither of them could qualify.

Numerous examinations of the pottery pigments were made and the results are included in tho table. The manganese base pigment is common to all or nearly all the Jeddito Black-on-Yellow. The few pieces of Black-on-yellow that have ether pigments than the manganese base possibly are not true Jeddito Black-on-Yellow. A number of copper base pigments were found on other types of pottery. Copper with maganese, copper with lead, copper with lead and manganese. One piece with a black copper paint was heated to 1100 degrees C. in a current of hydrogen. After this treatment the copper showed up as rose colored metallic copper. The spectroscope does not show carbon, since graphite electrodes are used. While carbon may be present all or some of the pigments designated as manganese base, I am sure that the carbon is present in very minor amounts, if at all, because the manganese lines are so intense.

The hydrofluoric acid test on black pigments followed by heating to bright redness in the muffle was used on some of the sherds, the pigments of which could not be identified by means of the spectroscope. In all cases the pigment was found to be carbon by itself or with manganese or iron.

Generally speaking, the spectroscope shows the Jeddito Black-on-Yellow pottery, sherds of which have been examined, to have been made from clays of very low manganese content, quite low calcium and copper content, and fair amounts of sodiim and chromium. (I am still speaking of comparative amounts according to the spectroscope, and not percentages). If anything more is to be done in determining where this class of pottery was made, it will be necessary to obtain clay samples from many different districts.

POTSHERD DATA
(Spectrographic Relative Intensities)

TZG - Tuzigoot
TAP - Tapco. Small six room pueblo below Tapco in Verde Valley.
SCV - South Cornville Ruin
SPC - Spring Creek Ruin
NA - Museum of Northern Arizona