Metal Finishing Guide Book

2011-2012 Surface Finishing Guidebook

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surface treatments ANTIQUING OF BRASS, COPPER, AND BRONZE BY MARK RUHLAND BIRCHWOOD CASEY, MINNEAPOLIS; www.birchwoodcasey.com It's been said that "Beauty is in the eye of the beholder" and nowhere is this more true than in the antique hardware industry. Antique finishes have long been a pop- ular option offered by manufacturers of decorative hardware of all types including lighting fixtures, locks, cabinet hardware, fasteners, and many other decorative items (see Fig. 1). Market demand for these finishes soared in the 1970s, leading to the development of efficient production-scale processing techniques. Since that time the demand has waxed and waned with the vagaries of the market. Regardless of the popular choices of the marketplace, there will always be a demand for high-qual- ity antique-finished hardware. This discussion will provide an overview of the various processes involved in the production of antique finishes. There are several different options available to the finisher at each step of the process and choices to be made, depending on relative efficiencies, operating cost, pollution implications, subsequent operations, etc. Consequently, the preferred process steps can vary widely from one plant to another. The process begins with the substrate. SUBSTRATE METALS IN COMMON USE There are three types of materials in common use. Solid Brass, Bronze, or Copper Available in several forms, these materials are commonly employed in outdoor appli- cations or high-quality indoor applications. Since these alloys tend to form protective oxide films they have come to be the materials of choice for items such as outdoor lighting fixtures, locks, marine hardware, building trim, statuary items, certain fas- teners, and other decorative items. This protective oxide film presents the finish- er or designer with two options with respect to the finishing of the article: the piece can be given an "artificial" antique finish, which is preserved by outdoor-grade lac- quers; or the article can be given an initial antique finish with only a temporary top- coat, which allows the surface to age naturally in service. This naturally devel- oped oxide or patina is often more attractive than those artificially produced and is preferable for certain items such as builders' hardware, statuary, and some light fixtures. There are several grades of these base metals employed in manufacturing the items described above. Solid grades of brass and copper sheet stock in varying alloys are used to manufacture light fixtures, fascia panels, and roofing for building construction, stamped or drawn fasteners, and other items that require malleability for ease of forming. Cast grades of brass and bronze are widely used for statuary, plaques, or high-quality hardware. Many of these items are further machined, polished, or belt sanded to form the final outer surface, which is then given an antique finish. Steel Stampings, Spinnings, or Machined Items Steel is often used in applications requiring higher load-bearing capacity than 382

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