Rocks as blue, green and black pigments/dyes of glazed pottery and enamelled glass artefacts ? A review

Abstract

Among the four different ways (and their combinations) to colour a solid, the dispersion of a phase, already coloured and stable in the fired/molten matrix – a pigment – is the technique offering the largest palette. The pigment preparation involves sophisticated high-temperature routes and/or the use of selected, sometimes rare minerals. Consequently, ancient painters, potters, craftsmen and glassmakers selected natural rocks or minerals to obtain blue, green, red and black colours. For instance, the blue coloration requires the use of a rare element: cobalt. Pure cobalt ores spots were exceptional and the difficult purification of cobalt derivatives could be obtained during the 19th century only. Thus, potters and glassmakers solved the problem by using recycling or specific minerals, for instance lapis lazuli, and developed convenient techniques with the use of mixed ores to obtain the blue, green, red or black colour. We discuss here enamelling/glazing technologies of ceramic and glass masterpieces with emphasis on the lapis lazuli use as blue or green pigment. We will reveal how the recent Raman microscopy studies deeply change our knowledge on the history of colouring techniques.