![]() ![]() The cleaning should be done using a fairly stiff short-bristled cleaning brush in the direction of the grain. This not only cleans the surface but enhances the cutting quality of abrasives if subsequent mechanical finishing is to be done before applying the colour.Ĭlean to a bright satin finish using a mixture of 5% oxalic acid and water together with fine India pumice powder. The metal surface should be degreased with trichloroethylene or similar solvents. In any case, the sulfide solution employed should be fairly dilute, since concentrated solutions can result in a brittle film that may be non-adherent. The desirable contrast in colour can be produced by scratch brushing with a pumice paste, or by use of a "greaseless" polishing compound on a buffing wheel. Modifications of these formulas called for the use of sodium, potassium, barium, and ammonium sulfides, which were claimed to produce different shades, but almost all sulfide colours are now produced from solutions of polysulfides which are sold in the concentrated form under a number of trade names, usually called "oxidizing liquid."Īll sulfide films require wet or dry scratch brushing for a good appearance and will look better longer if protected by oiling, waxing or, more permanently, by a good top coat of clear lacquer. Originally liver of sulfur was employed, this being a crude mixture of potassium polysulfides and thiosulfate, also called potassium sulfuret. The use of chemical solutions is generally termed "oxidizing," although the oldest method and the one which produces the widest range of brown to black stages on copper alloys actually produces not an oxide but a metal sulfide finish by the use of alkaline sulfide solutions. In conversion coatings, the metal surface is either converted into a protective film, usually, an oxide or sulfide of the metal involved, or a compound is precipitated which forms a surface film. Statuary finishes are conversion coatings. This datasheet presents the technology which underlies the craftsmanship and art involved in producing these coloured finishes. ![]() Chemical colouring techniques depend upon time, temperature, surface preparation, the mineral content of the water, humidity and other variables which influence the ultimate result. The wide range of colours and shades which may be achieved is largely a matter of craftsmanship and experience. While the chemical solutions described are those generally accepted in the metal finishing trade, many variations exist. This data sheet outlines procedures and formulations for producing both. While these metals may be used in their natural colour, as fabricated, it is sometimes desirable to chemically colour pure copper (UNS C11000), commercial bronze (UNS C22000), architectural bronze (UNS C38500) or other alloys referred to as "bronze" in architectural parlance The most common colours to be produced are referred to as brown or statuary finishes for bronze and green or copper patina finishes for copper. Please contact Austral Wright Metals for details of Factory Pre-Patinated Copper Architecture.Ĭopper and copper alloys are widely used in architectural applications to take advantage of their inherent range of colours of patina on copper. Since some of the pre-patinated sheets have a variation in their final colour, it is recommended that the architect review material samples before final specifications. The patina is a chemical conversion process whereby the top molecular surface of the copper sheet is enhanced and forced to produce a natural patina. The large number of requests by the architectural community for a man-made copper patina has prompted copper mills to research and develop pre-patinated copper sheet products. In arid desert environments, the patina formation may never occur and the copper surface may remain a dark brown or bronze colour. In rural atmospheres, with relatively clean air patina formation may occur in 10 to 14 years. In industrial and marine atmospheres, the natural patina generally forms in 5 to 7 years. ![]() The natural weathering of copper from its bright pink to the characteristic blue-green colour (patina) is a direct consequence of its reaction to the corrosive action of the atmosphere. Factory Pre-Patinated Copper Table of Contents ![]()
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