Stamps were large machines that crushed tin or copper ore, pulverising small lumps into a sand-like material. Each stamp was made from heavy timber with an iron head at the bottom. A rotating axle with cams raised the head and dropped it onto the ore, and water washed it into a box beneath. The heads, weighing between 4 and 8 cwt (200–400 kgs) each, were arranged in sets of four in timber frames. Small stamps could be powered by water wheels and larger ones by steam engines. Before the stamps were used, the work was done manually by women known as bal-maidens. The stamps used in Cornwall in the early 19th century were usually water powered. Steam power was first used to drive the stamps in 1813 at Wheal Fanny on Carn Brae.
Californian stamps were introduced in America during the gold rush of the late 1840s. They differed from the Cornish stamps design in having five circular, not four square heads. After 1857 better-performing Californian stamps began to be used in Cornwall. Stamps were manufactured locally by Harvey’s of Hayle and the Perran FoundryCornish foundry established in 1791 to supply steam-engine pumps and heavy machinery to mines, waterworks and ironworks..