Fig. 5From: Beautiful Pietàs in South Tyrol (Northern Italy): local or imported works of art?In the centre a hydrated grain of firing products with carbonatic impurities—exhibiting bright, pastel interference colours due to the extremely high birefringence of calcite and dolomite—in the mortar sample belonging to the Pietà in the Chapel St. Ann in Mölten (transmitted light, parallel/crossed Nicols)Back to article page