Bone Ash, white

thickening extender in lime paints

• Chemical description: Bone Ash (CaO 52%, P2O2 40%, SiO2 2%)
• Suitability: Acrylics, Lime / Fresco, Silicate binder, Waterglass

Chemical composition: tricalcium phosphate Ca3(PO4)2 Bone ash is made by calcining animal bones. It often contains additional traces of calcium carbonate and other minor constituents. Ash from the bones of different animals varies a little in composition. Bone ash is a grayish white, slightly gritty powder. For the silver point technique, it was used for its abrasive properties and tooth on paper and parchment in medieval times. Excerpts from: Painting Materials by Rutherford J. Gettens and George L. Stout