SEM study of black, blue, violet and yellow inglaze colours of the oldest Swiss tin‐opacified stove tiles (c.1450–c.1512, canton Bern)*

Abstract

The ceramic colours of eight late medieval to early Renaissance stove tiles were studied by scanning electron microscopy‐backscattered electron (SEM‐BSE) images and SEM with energy‐dispersive spectroscopy (SEM‐EDS). Microstructural observations and chemical compositions of these colours give some insight into the colouring agents and techniques used by the potters. All decorations were applied as inglaze opaque colours on the unfired powdery tin‐opacified glaze. The base glass was a Si‐Pb glass, that is, for the blue, not a K‐rich smalt. Two Co blue, with or without relics of Fe‐Co‐Ni and Ni‐Co spinels (‘safre’), could be distinguished. Pb‐Sn‐Sb triple oxide was used for the yellow. The violet was obtained by adding some Mn to the tin‐opacified glaze. The black was either a Mn‐doped blue or a CuO‐SnO2 black. The colours were probably purchased and not locally prepared.