Archaeometry 48 (2)

The work applies established analytical techniques from the physical sciences to Irish brick, in order to gather evidence of ceramic technologies, provenance and sources of raw materials. Petrographic microscopy, X-ray diffractometry and scanning electron microscopy with an energy-dispersive X-ray diffraction attachment were used to study the brick of Rathfarham Castle, Dublin, built c. 1618, where clay brick was introduced in 1771. Local clay was fired in the laboratory and analysed in a similar manner. The petrography of the pointing mortar was studied in order to gather evidence of ceramic provenance. The paper concludes that the brick was hand-moulded with a silica-based, predominantly non-calcareous clay of glacial origin, gathered locally, including fluxes and a high percentage of non-plastic material. The mineralogy and petrography of the brick, together with the presence of pebbles and a coarse matrix, suggest that the raw clay was probably gathered from a glacial deposit. The presence of abundant pebbles and colour inhomogeneities suggests a lack of processing of the raw clay. The brick was probably fired in clamps at top firing temperatures ranging from 750°C to above 900°C. Transformation of limestone temper involving the breakdown of calcite and the generation of calcium silicates, and the new formation of plagioclase, high-temperature quartz, hematite and spinel were revealed. The presence of spinel in `hot spots' indicates that fuel was added to the raw clay in order to assist firing.

The study highlights regional variation in the composition of iron-smelting slag produced in England prior to the medieval period and attempts to link slag composition to the type of ore smelted. For many sites, the slag compositions were consistent with the use of limonite ore, but there is evidence that siderite ore was smelted at sites in Sussex in the Late Iron Age/Romano-British periods. A compositional comparison of smelting slags and slag inclusions in Iron Age currency bars, using data from Hedges and Salter (1979), illustrates the potential of smelting slag compositional data in provenance studies of early iron objects.

Contrasting lifestyles are recorded by the isotope composition of Bronze Age Beaker people (c. 2500--2000 bc) from three burial sites (Boscombe Down, Normanton Down and the ditch around Stonehenge) at or near to the Stonehenge monument in Wiltshire. Seven individuals (three adults, a sub-adult, two juveniles and an infant) were recovered from a single grave at Boscombe Down. Strontium and oxygen isotope analysis of tooth enamel from two teeth (a premolar and third molar) from each of three of the adults in this grave (referred to as Boscombe Bowmen) show that they had all shared a pattern of mobility and migration during their lives. The three adult males spent their early childhood (as represented by data from the premolar teeth) in an area with a radiogenic 87Sr/86Sr isotope signature of around 0.7135. They each then moved, during early adolescence (as represented by the third molar results), to a less radiogenic area, where they acquired an 87Sr/86Sr signature of around 0.7112. This implies that they must then have travelled to the Stonehenge area of Wiltshire at a later time in their lives. Wales provides the closest area with rocks that supply suitable 87Sr/86Sr ratios and 18O isotope compositions for these individuals, although other areas of Palaeozoic rock, such as Scotland and parts of Europe, cannot be ruled out. Enamel from the two juveniles from the Boscombe Down burial yields 87Sr/86Sr ratios of 0.7098 and 0.7099, and strontium concentrations for both of 55 ppm. The very close match of the data for the two juveniles supports the possibility that they were raised in the same environment. The difference in strontium isotope data between the juveniles and three adult males described above shows that the children did not come from the same homeland as the adults with whom they share a grave. The two adult males from the single burials at Normanton Down, and from Stonehenge itself, had static lifestyles and show no evidence of migration, in contrast to the Boscombe Bowmen. Their oxygen and strontium data are consistent with a childhood in the Stonehenge area.