 Graduation tower

A graduation tower (occasionally referred to as a thorn house) is a structure used in the production of salt which removes water from a saline solution by evaporation, increasing its concentration of mineral salts.The tower consists of a wooden wall-like frame stuffed with bundles of brushwood (typically blackthorn) which have to be changed about every 5 to 10 years as they become encrusted with mineral deposits over time.