Bronze Age Bling: Black Stone, Amber and Shells

A 4,200-year-old necklace made of alternating black and white disc-shaped beads has helped British researchers devise a new, minimally micro-destructive approach for the identification of shell species in archaeological artifacts.

Mollusc shells appear to have been among the first durable materials used for personal ornaments and building tools, but their often degraded condition makes it hard to identify the shell species taxa with traditional morphological analysis.

Beatrice Demarchi, of York University’s department of Archaeology, Julie Wilson, of York University’s departments of Chemistry and Mathematics, and colleagues used statistical pattern recognition methods and amino acid racemisation analysis (a technique previously adopted used for dating rocks and fossil molluscs) to distinguish shells taxonomically.

“Shells preserve organic molecules trapped within the mineral skeleton, particularly proteins that are responsible for the process of biomineralisation,” they wrote in the journal PLOS ONE.

The new approach was tested on a necklace which has intrigued archaeologists ever since its discovery in 2009.

Found at an early Bronze Age site in Great Cornard, near Suffolk in eastern England, the necklace was unearthed by a team of archaeologists of Suffolk County Council Archaeology Service in the grave of a young adult woman. Her bones were radiocarbon-dated to around 2200 B.C.

“The necklace had not been worn on the body, but was found near the head. On the other side of the head was a Beaker pot which had probably contained drink for the journey into the afterlife,” Alison Sheridan, principal curator of Early Prehistory at National Museums in Scotland, told Discovery News.

The necklace consisted of strings of tiny disc beads of shells and black Whitby jet (a semi-precious stone which, when polished, takes on a waxy luster of the deepest opaque black), possibly carved out of the fossils of monkey puzzle trees at Whitby some 160 miles north.

“Beads of jet and shell alternated in a zebra design. Interspersed with these — and I am currently trying to work out exactly how the arrangement worked — were a number of amber beads, some perforated straight through, some with cross-shaped perforations,” Sheridan said.

She noted that both the amber and the jet would have been accorded magical properties and used as amulets, to ward off evil and protect the woman.

“The necklace design is unique, although a lot of Early Bronze Age jet jewellery, and some amber jewellery, is known,” Sheridan said.

“However, the use of sea shells for jewellery during the Early Bronze Age in Britain is incredibly rare,” she added.

To determine whether the tiny beads were made from locally sourced shells or from species originating from further afield, such as the Mediterranean thorny oyster (Spondylus) often used to make personal adornments in prehistory, the researchers sampled six of the necklace’s beads.

Demarchi and colleagues compared the beads’ amino acid concentrations with a data set comprising 777 molluscan samples. The investigation was integrated with morphological observations by electron and light microscopy and mineralogical examinations by Raman spectroscopy.

From the results, it appears that Bronze Age craftspeople used local shells like dog whelk (Nucella lapillus) and tusk shells (Antalis) to make the necklace.

Conical, curved and open at both ends, tusk shells resemble miniature elephant tusks, hence the name. Dog whelks are predatory, carnivorous sea snails often found on rocky shores.

While dog whelks are abundant around the Suffolk coast today, tusk shells are less widespread but present along the southern coast. According to the researchers, both shells were likely to have been sourced and worked locally.

“Now we have a relatively simple and only micro-destructive approach that provides information about the raw materials used for these precious and rare artifacts,” Julie Wilson told Discovery News.

Read more at Discovery News