Copper is available in sheet and pipe form, and is known for its green patina (popularly called "verdigris") of copper sulphate and copper carbonate which forms within a few weeks of the metal being exposed to moisture and the weather. Copper is half the weight of lead and is relatively non-toxic (verdigris, however, is harmful). Because of its good electroconductivity, it is used for lightning conductors (including those for trees). It can be cast and welded, may be rolled or drawn, and has a melting point of 1,981.4ºF. Copper is good as a roofing and cladding material, for pipes and tubes, for copings on brick walls, as a cover for lumber posts, as a flashing for water features, and also for moisture-proof courses.