Is there some way to test if an object is brass or bronze? I vaguely remember somebody telling me about a magnet test but I forgot which is which. Anybody know a trick?
posted on October 13, 2003 09:46:20 AM new
You may have heard: You can use a magnet. If it is brass a magnet will not attract.
However, unless I am mistaken, there is no reliable magnetic test.
Manganese is the component in bronzes that make them magnetic. Only a few bronzes contain manganese, most bronzes do not.
Further, brass tends to be a trash-y metal; it is not uncommon to find magnetic contaminates in brass.
Brass is an alloy of copper and zinc, about 70% copper. Bronze is mostly copper, with small amounts of tin and zinc to alter its melting and casting characteristics. Brass tends to be used in objects that are rolled, machined, drawn or spun. Bronze is preferred for casting. Brass objects are often polished and lacquered to maintain the yellow color. Medical and scientific instruments are typical. Bronze objects are most often patinaed, naturally or chemically. Copper alloys differ from iron and its alloys in the way it reacts to mechanical working. Iron alloys tend to become softer as they're hammer worked and are tempered to reharden. Copper alloys become more brittle when hammered and have to be periodically reheated to make them malleable.
There's no definitive test, other than a metallurgical analysis. The proportions of metals used in the alloy can vary, depending on maker preference and availability, so there's considerable grey area, but in better objects you can pretty well count on the method used to craft the object to predict whether the metal is closer to brass or bronze.
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[ edited by gousainc on Oct 13, 2003 10:53 AM ]
posted on October 14, 2003 09:43:49 PM new
I don't know how to tell bronze from brass but according to the Marine Metals Manual by Roger Pretzer, "Bronze differs from brass in that bronze has a high copper content (90% or above) and .... its three main alloying elements are either tin, aluminum or silicon." He goes on to say "there are many other elements besides, and including, the above three that are added to copper to form the multitude of bronzes."
"Add zinc to copper (anywhere from 5% to over 40%) and sometimes add a small percentage of another element such as lead, tin, or manganese and iron and you have the makings of the large variety of brasses."
