This section is from the book "A Treatise On Architecture And Building Construction Vol3: Stair Building, Ornamental Ironwork, Roofing, Sheet-Metal Work, Electric-Light Wiring And Bellwork", by The Colliery Engineer Co.. Also available from Amazon: A Treatise On Architecture And Building Construction.
Copper is, obtained from its ore by the following process: First, the ore is roasted or calcined; after the roasting, it is melted in a reverberatory furnace, whence it issues in the state called coarse metal; this metal is then stamped and pulverized, passed through a furnace, and afterwards melted; the resulting pure metal is roasted and then refined. The copper is then cast into ingots and afterwards rolled into sheets, which are cut to market sizes, varying from 24 in. X 48 in. to 48 in. X 72 in., and are supplied in two forms, soft or annealed, and hard or cold rolled. Both varieties may be tin plated or "tinned," when desired.
The qualities determining the suitability of the sheets for roofing are ductility and strength, and uniformity of gauge or thickness. The sheets must stand bending with and across the fiber, without yielding even to repeated attempts at splitting and breaking. The gauge, which varies from 1 to 30, must be as represented, and tested with a wire gauge, and the sheet must be of the full weight, corresponding to the gauge, which, in common use, ranges from 10 to 20 ounces per square foot. When a piece is broken off, the fiber should present a bright, lustrous, and silky appearance, if the copper is of the best grade. The metal should also bear stamping into form without developing fractures.