<P> Copper and its alloys can be' finished' to embark a particular look, feel, and / or color . Finishes include mechanical surface treatments, chemical coloring, and coatings . These are described here . </P> <P> Mechanical surface treatments . Several types of mechanical surface treatments exist . Mill finishes are derived by normal production processes, such as rolling, extrusion, or casting . "Buffeted" finishes impart bright mirror - like appearances after grinding, polishing, and buffing . "Directional textured" finishes provide a smooth, velvety satin sheen in a continuous pattern of fine nearly parallel scratches . "Non-directional textured matte" finishes achieve a rough texture, primarily on castings, as spray sand or metal shot are applied under high pressure . And "patterned" finishes, made by pressing a copper alloy sheet between two rolls, produce a textured and embossed look . </P> <P> Chemically induced patina . Architects sometimes request a particular patina color at installation . Factory - applied chemically induced pre-patination systems can produce a wide range of colored finishes similar to natural patination . Pre-patinated copper is particularly useful in repairs when there is need to provide close color matches to old copper roofs . Pre-patination is also considered in some modern building materials, such as vertical cladding, soffits, and gutters where patination is desired but would not ordinarily occur . </P> <P> Chemical coloring of metals is an art involving craftsmanship and experience . Coloring techniques depend upon time, temperature, surface preparation, humidity and other variables . Pre-patinated copper sheets are produced by fabricators under controlled environments using patented chemical processes . Green patina finishes are primarily developed using acid chloride or acid sulfate . Treatments with ammonium chloride (sal ammoniac), cuprous chloride / hydrochloric acid, and ammonium sulfate are somewhat successful . Statuary finishes can be produced in light, medium, and dark brown, depending on the concentration and number of coloring applications . One advantage is that the treatment disguises surface markings on bright mill finish copper and can advance the natural patination process . </P>

Where does the copper come from that ends up on the nickel strip