Ash glaze made of wood ash and brown coal ash fired at c. 1200 °C, Rolf Overberg, Osnabrück 1960, photo by Wolf Matthes.

Glaze made of glass powder, wood ash, rice husk ash and limestone powder, dyed using copper carbonate and a small amount of cobalt oxide; stoneware-fired at c. 1220°C in a multi-chambered kiln fuelled by wood; from a workshop in Binh-Duc, Vietnam 2000, photo by Wolf Matthes.

Because plants mainly need calcium, magnesium, potassium, phosphorus, iron and manganese to grow, plant ash is an interesting component when added to glaze formulas, particularly in stoneware glazes that are fired between 1200°C and 1350°C. Plant ash acts as a fluxing agent and the resulting glazes are of very different colours and transparency.

Translation Sandy Haemmerle

German: Ascheglasur

French: glaçure aux cendres

References:

Wolf Matthes, Keramische Glasuren 2, Koblenz 2012, 21–34.