Is Brass Magnetic? What Is Magnetic Brass?
The short and skinny answer? No, brass is non-magnetic.
But, there are some very real circumstances that cause genuine brass to be magnetic. It is not actually the brass that is magnetic, per se. Let me explain:
What Is Brass?
Brass is defined as an alloy of copper (Cu) and zinc (Zn). Traditionally, yellow brass is made up of 66.7% copper (Cu) and 33.3% zinc (Zn). Yellow brass is named so for its easily recognizable yellow luster.
Most commercial brass goods are made from a brass alloy with proportions similar to traditional yellow brass, although it is very common to find brass w/ additives, for example lead (Pb) or nickel (Ni).
Brass is used commercially to make anything from valves to bells. In the photo above, you can see the chemical analysis of the yellow brass found in a scrap cymbal from a cheap drum set.
What Is Magnetic Brass?
99 times out of 100, if something sticks to a magnet, then it is not brass. That is a rule of thumb that has saved me from looking like an idiot at the scrap yard many times.
If something looks like brass but sticks to a magnet, then it is probably plain steel that has been electroplated with a thin coating of brass; it’s possible, also, that it is genuine brass with a piece of steel inside to improve its strength; Or, sometimes brass items have a thick chrome plating, in which case the various layers of plating may be very slightly magnetic.
There are, however, circumstances when the actual brass alloy has significant Iron (Fe) content mixed in, in which case the brass alloy itself will be noticeably magnetic.
Iron, nickel, and cobalt are the only elements that stick to a magnet. If something is magnetic, they must contain one of those elements. Steel, for example, contains iron, that is why it is magnetic.
The above picture shows a rare-earth magnet sticking to a genuine brass casting on a scrap chandelier. I thoroughly examined this brass casting, and found no steel anywhere. No hardware, nothing. I even cut it in half, but all I found inside was yellow colored brass.
I knew intuitively that it was a genuine brass alloy because when I hit it with a wrench it rang out – sort of like a bell. This is an extremely reliable method for identifying copper alloys once you have some experience with it.
I decided to have the metal chemically analyzed because my curiosity was killing me.
The above chemical analysis is called XRF analysis, and it can be done at any reputable scrap yard. They first grind away the surface of the sample (to remove oxidation, grease, general contamination) and then shoot it with X-rays. The surface reaction is measured, and then the contents of the alloy can be narrowed down using statistics. This method of analysis is surprisingly accurate, and it takes only seconds.
The analysis showed that my intuition was correct: I had a genuine brass alloy. However, it was noticeably light on copper content and had significant additives, including about 1% iron (Fe). This iron content is what allowed the magnet to stick to the brass.
Crazy, right? Genuine brass can be magnetic, but only if it has Iron (Fe) added to the alloy. In this case, with a rare-earth magnet, all it took was 1% iron.
From the little research I’ve done, adding cobalt should also make a brass alloy noticeably magnetic, although there is no such alloy used in industry today. The only way I can test this is to make my own brass/cobalt alloy, which I may try at a later time.
In case you are wondering, nickel is also magnetic but that is not the culprit. Nickel/copper alloys are not magnetic. (Think of US 5 cent coins aka nickels, which are made from cupronickel… They are not magnetic, and neither is nickel silver, commonly used in silver plated goods.)
Why Do Some Brass Alloys Have Iron In Them?
The brass alloy above is most likely made from cheap recycled brass which contains traces of iron. Many brass alloy specifications allow for up to 1% iron, and some brass alloy specifications even require iron to be added to improve corrosion resistance and strength.
Please share your questions, insights, ideas, and tips in the comments. Happy Scrapping.