The petrographic laboratory of the Israel Antiquities Authority (IAA) runs petrographic studies of pottery and other clay objects since 1990. The laboratory is equipped with a Hillquist thin section machine and Buehler grinder polisher unit for preparation of 30µm-thick thin sections. The thin sections are studied under a Nikon (Labophot-pol) and Zeiss (Axio Scope A1) petrographic (polarizing) microscopes. Photomicrographs are taken by a digital camera coupled to the microscopes. A Leica stereomicroscope is also used to examine fresh breaks.
The material analyzed is mainly from the Levant and extends chronologically from the beginning of pottery production in the Neolithic Period to Medieval Times. The projects are derived of archaeological questions concerning provenance and technology of pottery and clay artifacts.
Our database includes a large collection of comparative thin sections from most of the key sites in Israel. The collection includes samples from production sites, which are valuable for characterizing the fabrics from a single workshop, and serve as a reference for local raw materials. In addition, the comparative collection includes thin sections made of hand-samples of potentially raw materials taken from exposed clay units. These hand-samples were moistened and shaped into small briquettes and after drying were fired in a pottery kiln. Subsequently, a thin-section was prepared from each briquette and examined under the petrographic microscope.
The IAA petrographic laboratory is collaborating with colleagues from research institutes, universities and excavation expeditions by contracts and financial arrangements.
Petrographic researcher:
Petrographic analysis is a technique developed in the earth-sciences for observing and identifying rocks and minerals. It involves creating a "thin-section" of the material being studied, which is a thin slice exactly 0.03 mm (300µm) thick. Once the thin-section is made it is viewed through a polarizing microscope, which has two polarizing filters oriented at right-angles to each other, thereby blocking out any light. However, a sample containing minerals may diffract the light, so that they are visible in cross-polarized light. The degree of diffraction is a key characteristic enabling identification of mineral components in pottery. This information is then usually used to tie the artifacts to geological source areas for both the clay used and the rock fragments (usually called "temper" "inclusions" or "aplastics") that can naturally occur in the clayey sediment used but often deliberately added by potters to modify the properties of the clay. This information could be effectively used to answer archaeological questions concerning provenance and technology. The petrographic research provides insight into how potters were selecting and using local and non-local resources, as well as allowing archaeologist to determine whether pottery found in a particular location was locally produced or traded from elsewhere. In turn, this kind of information (in combination with other evidence) can be used to build inferences about settlement patterns, group and individual mobility, and social contacts or trade networks. In addition, the petrography can answer technological questions such as the temperature reached in the firing of the pot and how it was constructed (e.g., by hand or wheel).