Tin produced in Cornish mines frequently contained arsenic and sulphur. These elements were detrimental to smelted tin and therefore had to be removed by roasting - this was done in burning houses or calciners ,
the vapour given off condensed on the walls of long stone tunnels called labyrinths.
The miners then scraped the deposits of the chamber walls , the chimney releasing the remaining fumes.
Location: SW 3558 3273