Crazing Mill Stone at Gobbet Blowing House

This photograph is dated 7 March 1888. It shows evidence of the tin mining industry which operated on Dartmoor until around 1939. Blowing houses (sometimes called blowing mills) contained small blast furnaces into which a forced draught of air was blown using waterwheel-powered bellows. Cassiterite (tin oxide) ore was smelted in the blast furnace and cast into ingots using a mould stone. The round stone is a crazing mill stone. They were used for grinding the tin ore between two flat-faced circular stones. Crazing mills could only grind the alluvial gravels and they were replaced by stamping mills when coarser ores started being mined. Gobbett is one of only three crazing mill remains on Dartmoor.