Muntz Metal: Modern Brass
Muntz metal is a copper alloy made using primarily copper (60%), zinc (40%), and traces of iron. As a copper-zinc alloy, it falls under the brasses, and is used frequently by designers seeking an alloy that exhibits the elegant soft golden tone. Muntz metal acquired its name from its inventor, George F. Muntz, who developed the alloy for the lining of boat hulls in 1832.
Muntz metal is very durable. This alloy falls at the start of the alpha/beta transition, and thus its behavior under stresses varies from that of the ductile Yellow Brass and Cartridge Brass. Cold working is possible but difficult. The downside of alpha/beta brasses, si that the alloy will crack under severe cold-working operations. Welding and brazing this alloy is not an easy task. It is also at risk for dezincification corrosion, in which small dark pits appear in the failing metal surface.
Interstitial annealing is required to form severe shapes. The annealing generates oxides on the surface, which are difficult to remove. This alloy should be used for only limited cold-forming operations.
Under hot-forming operations this alloy performs well. Hot-forming processes are not commonly used for shaping architectural metal features. Hot forming will build up oxides on the surface, and discoloration of the surface will require post-polishing.
Using lower cold-rolled tempers does little to soften this hard alloy. Muntz metal can be polished to a mirror finish. Satin polishes and custom polishing are also possible with this striking architectural alloy. It will take statuary finishes in all the available ranges. When used on the exterior of a building, Muntz metal should be protected with a clear coating. There are only a few available cold-working tempers.
Maintaining the color on Muntz metal requires either periodic polishing or sealing the material. The bright reflective brass color of Muntz metal will fade, losing reflectivity, and develop over time into a gray-green patina.