What is ICP-MA/ES analysis?

Inductively coupled plasma-mass atomic emission spectrometry

ICP-MA/ES analyses is today the most reliable method for determine the provenance of ceramics, bricks, tiles and other artefacts made by clays.

ICP is an isotope analyse that provides information on the chemical identity of a sherd by measuring a vast spectrum of elements (Al, Ca, Ce, Co, Cr, Ga, La, Mg, Mn, Ma, Sr and V) down to extremely low concentrations. The basis for the analysis is that clays and soil from different areas have different chemical compositions and those that are similar are from the same site or area.

Many studies during the last 20 years have shown that it is usually possible to pinpoint a clay source within less than 10 kilometres.

For this type of study, it is essential to have comparative materials.

Ceramic Studies has over the years built up a database of ceramics and clays mainly from Europe; the database currently contains of about 20,000 samples from many different countries. The reference material includes waste materials from kiln sites, raw clays and different types of ceramic materials from archaeological excavations. By using this database is it possible to determine the provenance of the archaeological material.

Thin section analyses

The aim of thin section analyses is to determine the type of clay and temper and to identify other materials such as plant materials, bones, sea shells and slag.

In order to be used for comparative studies a thin section is made according to a standardised thickness of exactly 0.03 mm.

In a polarising microscope it is possible to identify minerals in the silt- and sand fractions. The microscopy is not only a petrographic study, but it also involves other aspects of the pottery craft. It is possible to study different structures in the ware, such as vessel forming techniques, clay type, to distinguish between added and natural temper as

well as the amount and grain size of this material, organic matter e.g. diatoms and plant material etc. Particular observations of specific minerals and other features of the temper and clay have been noted. Sherds with the same type of clay and temper are most likely from the same production area.

The analyse is by using a polarising microscope at magnifications between 25 xs and 630 xs, in parallel as well as in polarised light.

Thermal colour test

Hue
the attribute of a colour

Value
the property that describes the lightness or darkness

Chroma
a quality of color combining hue and saturation

The aim of the thermal analyses is to determine the original firing temperature of pottery, bricks, crucible, burned clays and other objects made by clays.

Thermal colour test (TCT) is a method based on colour changes of the clay during repeated firing in order to estimate the firing temperature. The Munsell Colour Chart system is used as a standard colour reference. The firing is carried out at intervals of 100°C until a temperature of 1100°C is reached. The sample is fired 15 minutes at every interval. The colour is coded according to: hue, value and chroma. Each of these values is recorded separately on a graph. It is essential to the test that the colour of the clay does not start changing until the original firing temperature has been exceeded, thus an estimate of the original firing temperature, within a 100°C interval may be recorded.