In the vicinity of Berne Minster in Switzerland, 500 fragments of numerous late gothic polychromed sandstone sculptures deliberately destroyed in 1528 were recovered. A preliminary study of the painting technique and materials showed that, among other pigments, azurite had been used. This particular pigment showed the presence of black products on the surface of its grains. As similar observations of blackish conversion of basic cupric carbonates on Swiss wall paintings had been made previously, a study into the nature of this product was carried out. The authors were able to show that azurite had converted into black cupric oxide (tenorite) when exposed to the slightly basic environment of the burial site. Identical conversion products could be obtained experimentally on both artificial and natural azurite.