A total of 23 pieces of pottery (ceramics) were recovered from Zatopec; one of these probably dates to the period of Spanish colonial activity in south-Central Texas (ca. AD 1600-1740 or so), while the rest are prehistoric in age. This material was analyzed in different ways to try to determine where the pots may have been made before they arrived at Zatopec, or if it could be concluded that they may have been made at or near the site. Ten sherds or pieces (9 Late Prehistoric and 1 Colonial) were analyzed for the elemental composition of the clay that was used. Eight of these 10 specimens were also described for their mineralogical content. All 23 sherds were also described in plain-sight.
Instrumental Neutron Activation Analysis (INAA)
This technique was used to measure the elemental content (like iron, potassium, and so on) of our Zatopec ceramic samples. Once measured, the composition of each sherd is compared against a database of previously analyzed samples from the United States and elsewhere; several studies of ceramics from Texas are included in this database. If a sherd shows highly comparable elemental content with other sherds in the database, researchers can conclude that they may have come from the same general region. This technique works by irradiating samples with neutrons so that some of the atomic constituents convert into artificially radioactive isotopes. These radioactive elements are then measured at specified intervals, and the results are characteristic of the nature and concentration of the original elements.
Unfortunately, the database of previously analyzed samples in Central Texas is rather small, and no really close matches were found among any of the 10 Zatopec sherds analyzed in this manner. Clearly, archaeologists still have a long ways to go before we understand prehistoric ceramic technologies in south-Central Texas during the Late Prehistoric period.
Descriptive and Petrographic Report
This portion of the ceramic analysis involves the description of the characteristics of all 23 sherds in plain-sight, as well as the description of eight sherds under a microscope. Ceramics (prehistoric to the present) have many traits that are particular to cultures or regions or even individual makers. Therefore, an accurate description made by a ceramic specialist is a powerful tool that, much like INAA, can help identify origin. For example, 19 of the 23 sherds exhibit smooth exteriors with scattered evidence of burnishing, which are traits characteristic of the Leon Plain Ware variety. Two other samples are classified as Doss Red Ware sherds, because of their red decoration or red wash/slip. Both of these are common types in Central Texas.
Petrographic analysis is the examination of a sliver of a sample beneath a microscope lens. This technique uses methods borrowed from geology and soil science, and is a means of describing temper (or the material from which the ceramic was made). It is a slightly more subjective analysis than INAA, with the results depending in part on how the analysts recognize important minerals within the sherd. However, it does produce quantifiable data for content and mineral size, shape, roundness, and frequency. Petrographic analysis revealed four basic paste groups: bone tempered; bone, micrite, and chert tempered; bone and chert tempered; and "fine" paste. These results will prove to be an important comparative record for future ceramic studies in and around San Marcos.