A forgotten technology: The production of artificial millstones for windmills in Sistan, southeastern Iran

Abstract The present study investigates for the first time a largely forgotten pyrotechnology for manufacturing artificial millstones for Persian windmills and querns from Islamic period Sistan, a region in southeastern Iran. The unusual characteristics of these materials result from melting a sand-clay mixture at high temperatures. A unique experimental and multianalytical method was developed to understand the heating-cooling regime for manufacturing artificial millstones and other technical details of their production. According to chemical and microstructural analyses, these materials were melted between 1150 °C and 1250 °C and kept there for a period of 14–20 h, to be subsequently cooled down by 10–50 °C/h. Our experimental results for reproducing the microstructure of these objects show that any other temperature regime would be unsuccessful for manufacturing a functional millstone for these huge windmills which are usually referred to as the first wind turbines in the history of technology.