Scientific Analyses

Penn Museum's Ceramics Lab

Dr Marie-Claude Boileau and graduate student Griselle Rodriguez examine a ceramic thin section at high magnification in Penn Museum’s Ceramics Lab, at the Center for the Analysis of Archaeological Materials

Applying scientific techniques to the analysis of archaeological pottery helps us gain a deeper understanding of how ceramic objects were made and used in prehistoric societies. 

When archaeologists study cultures that produced pottery, initial research focuses on classifying excavated ceramic objects and fragments (sherds) into “types”.  A pot is defined by a combination of characteristics related to materials used, shape and decoration. Pots that share attributes form a type. Types are then grouped together into a typology which charts change and variation of types over time and provides a chronological sequence for a given archaeological site. Pots made in a specific place and time share decorative types and thus represent a local ‘style’.  A typology is a useful starting point to help identify where a particular pot may have been made or if it was traded from another production area.

Scientific analyses go beyond typology to give us deeper insight into the choices that potters made during the production of pots–from the initial choice of raw materials (clays and temper) to the techniques used to form, decorate, and fire the final product. Scientific data gained from these analyses, combined with typological and contextual information (in situ evidence at a site), enrich our archaeological interpretations of the potter’s craft by identifying distinctive potting traditions and networks of exchange between communities.

Among the wide variety of scientific techniques applied to pottery analysis, these are currently being used to enrich our understanding of Ban Chiang pots:

Polarizing microscope

Polarizing microscope used in petrography in the Ceramics Lab at the Center for the Analysis for Archaeological Materials, Penn Museum.

Petrography  is an analytical technique that uses polarized light microscopy to examine the minerals and rock inclusions present in a ceramic thin-section. A thin-section is a slice of ceramic, thin enough to transmit light, that is taken from an artifact and mounted on a glass slide. The aim is to match the mineralogy of inclusions to specific geological areas. Petrographic analysis helps identify where ceramic objects were made, thus allowing archaeologists to study networks of interaction between different communities and regions. In addition, ceramic petrography provides data on raw material preparation (i.e. mixing of clays and temper), manufacturing and firing processes by examining the clay groundmass and the shape and sizes of pores. For example, initial petrographic analysis of Ban Chiang thin- sections shows that for some pots, clay was mixed in with rice husks in an effort to prevent shrinkage during drying and firing.

Computed radiography setup at the Freer/Sackler Gallery, Smithsonian Institution

The setup for computed radiography at the Freer/Sackler Gallery of the Smithsonian Institution where a selection of Ban Chiang pots were radiographed

Radiography is a non-destructive analytical technique that reveals the internal structure of objects. Because the techniques ancient potters used to form ancient pots were often masked by the decorative or finishing treatments on their surfaces, radiography provides valuable information about forming techniques not evident to the naked eye.  For Ban Chiang, radiographic images obtained with computed radiography helped identify those pots which were made by a combination of techniques, for example a lower body made out of a molded slab and an upper body made of superimposed coils.

Scanning Electron Microscopy (SEM).

Scanning Electron Microscopy (SEM). Dr. Doug Yates, Director, Nanoscale Characterization Facility and Anthropology graduate student Susannah Fishman using the SEM at Penn’s Nanoscale Facility (now in the Singh Center for Nanotechnology).

Scanning Electron Microscopy (SEM) uses a beam of electrons to gain information about a ceramics sample at very high magnification. With EDS (energy dispersive spectrometer) capability, it also provides information about elemental composition.  When pots are fired above ca. 900oC, processes of melting (sintering) and fusion (vitrification) start to happen. In sintering, the clay particles begin to stick to each other and proceed to melt and fuse with rising firing temperatures. The fusion stage or vitrification stage brings about a loss of porosity and a densification of the clay body. In the case of Ban Chiang pots, SEM-EDS was used to help identify specific ceramic inclusions, examine slip and paint layers, and revealed that clay particles did not start to melt during the firing process, confirming that Ban Chiang pots were low fired.

Nina Owczarek demonstrating pXRF

Nina Owczarek (Williams Associate Conservator, Penn Museum) demonstrating the use of pXRF to examine Ban Chiang pots, to Penn graduate students

Portable X-Ray Fluorescence (pXRF) is a nondestructive  technique used to analyze the elemental composition of materials applied to the surface of pots, such as slips and paints.  To date, a small sample of Ban Chiang pots with painted decoration have been analyzed to acquire information about pigments used to produce different colors.