Scientific analysis of seventh-century glass fragments from the Crypta Balbi in Rome

Inductively coupled plasma emission spectroscopy, reflectance spectroscopy and X-ray diffraction were used to study seventh-century AD glass fragments from the Crypta Balbi in Rome. All the samples were found to be silica-sod a-lime glasses. Iron determines the colour of blue-green, green and yellow- green transparent glasses; chemical composition suggests deliberate additio n of iron and/or manganese in about half the samples. Copper was found as t he main colourant in red, pale blue and blue-green opaque fragments; elemen tal copper acts as an opacifier in red glass, and calcium antimonate in whi te, pale blue and blue-green glasses. Detection of antimony in transparent fragments suggests recycling of opaque mosaic tesserae.