From the late second century AD to the end of the fourth century AD, black, shiny materials were popular in Britain and the Rhineland for the production of jewellery. In the past, in the absence of accurate, detailed analysis, all these products, irrespective of composition, have invariably been described as being made of ‘jet’. A project at the University of Newcastle upon Tyne, UK, has used the non-destructive technique of reflected light microscopy to identify the various black materials used by the Roman craftsmen. Long used for petrographic studies of coals and fossil fuels, this technique has proved very suitable for the analysis of small artefacts. The project initially focused on black objects from the area of Hadrian's Wall but was extended to look at objects from Rhineland sites as well as finds from other parts of Britain and the Continent. The project has revealed that a wide range of ‘jets’ and shales and varieties of coal from a diversity of geographical sources were used, and that the Rhineland objects were not carved from Whitby jet but from an unidentified source.