Introducing ceramics 7 – colour

By Roy Towers

One of the joys of working with ceramics within the UHI Archaeological Institute in Orkney is the opportunity to collaborate with colleagues, both within and further afield.

This is particularly important when high-tech analyses are required but it can also apply to distinctly low-tech investigations as the examples which follow, here and in the next section illustrate.

High-tech first.

Many of you know that we have colour at the Ness – on the stones of the structures and on some of the pottery. The colours on pottery are red, black and white. This should not have been a surprise as a reddish pigment was noted at Skara Brae many years ago. 

Bronze Age pottery in Aberdeenshire, Spain and Hungary also features coloured inlay, mostly of a white bone paste and applied to incised decorative patterns.  In the Neolithic period research into the Dutch Funnel Beaker West Group (TRB) also established a white burnt bone inlay.

At the Ness, the white colour is found on vessels with applied decoration and not on incised examples, which is interesting in itself.

The identity of the materials which produced the colour is important and, initially, seemed clear.

Analysis showed that the red/pink colour was haematite, an iron ore which is found in Orkney. The black colour was simply lamp-black or soot, perhaps applied with a fixative.

With all the other examples of white colour in Scotland (although not in the Neolithic) and Europe, the identification of the Ness white colouring should have proved simple. It was not.

Initial analyses suggested the presence of apatite, which is a component of bone, and this pointed to a burnt bone paste, as seen elsewhere. Unfortunately, there was not enough apatite to be certain.

To make matters worse, the white colour contained silicate materials from rock, which has no business being present in a bone paste.

At this point Dr Richard Jones and colleagues from Glasgow University and elsewhere, mentioned already in an earlier piece, became involved.

I’m not going to pretend to understand the analyses he conducted. They were explained to me but thankfully not retained.

Here are some examples. Elemental analyses were carried out by portable X-ray fluorescence with real time digital processing and an Edax Oxford Microanalysis system attached to a Zeiss Sigma field-emission analytical SEM.

A Hitachi S-2700 SEM with an Oxford Inca 350 analyser at the Advanced Materials Research Laboratory at Strathclyde University was also involved, and for FITR and powder X-ray diffraction a Bruker D8 Advance using Cu Ka radiation with a  Sol-X Energy Dispersive detector and TOPAS 3.0 Rietveld analysis software were deployed.

You want more?

Raman spectra were obtained with a laser Raman microscope and (the only bit I understand) petrographic samples were examined with the intriguingly-named Leica Wild M240 polarising microscope.

This is serious high-tech scientific kit and, no, we don’t have any in Orkney, which is why we are so grateful to Dr Jones and his colleagues.

Solutions to the problems were forthcoming. The white colour is, indeed, a burnt bone paste.

The small amount of apatite present is probably because wet burial conditions at the Ness allowed microbial attack on the bone component.

The presence of silicate materials is likely to have come when the bone was ground down in a stone mortar, thereby incorporating tiny rock fragments into the resulting bone paste.

All of the above was a rollercoaster ride over five years or so and, despite the technical complexities, it was enormously exciting.

If anyone would like to read the exact details they can be found in a paper we published in the Journal of Archaeological Sciences: Reports 28 (2019) 102014  entitled Analysis of coloured Grooved Ware sherds from the Ness of Brodgar, Orkney.

Our next pottery story concerns an explosive (literally) account of prehistoric pots which refused to boil.