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 by designers seeking an alloy that exhibits a grey-yellow tone for interiors. 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 best suited for interior application and fewer lower stress exterior applications. This alloy is the highest numbered brass alloy and is at the extreme end of the beta phase. For this reason, its behavior under stress diverges from that of the ductile Yellow Brass and Cartridge Brass. It is also at risk for dezincification corrosion, in which small dark pits appear in the failing metal surface. Stress fracture corrosion is another concern that must be considered.
Cold-working this material is possible but difficult. The downside of alpha/beta brasses, is that the alloy will crack under severe cold-working operations. Interstitial annealing is required to form severe shapes. The annealing generates oxides on the surface, which are difficult to remove.
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. However, welding and brazing this alloy is not an easy task and should be done with care.
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.