Learn the one thing that distinguishes it from brass, according to appraisers.

By Roxanna Coldiron
July 24, 2019
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Copper, with its rich caramel hue, adds a charming warmth to your home. And as any collector knows, cleaning and polishing your copper pieces on a regular basis keeps them from looking dull and tarnished. Copper's value derives from its beautiful reddish-gold shade, its strength and corrosion resistance, and its malleability into other shapes. You can find copper in household fixtures, the pipes of your building, in jewelry and even artwork.

But copper's benefits go beyond the aesthetic: The chemical element and metal contains antibacterial properties that make it ideal for preventing the growth of certain fungi and bacteria like E. Coli, MRSA, and legionella. Copper can also bond with other metals. It's also conductive, which is why it is used in electrical wiring. With its plethora of uses, you will want to be sure that your item is the real deal. What are some of the things you should look for when examining a piece for copper while perusing an estate sale, the flea market, or yard sales on Saturday morning?

The Color Test

Copper and brass are easily confused because they look so similar. "Copper has a natural pink tone with reddish-brown hue like a newly minted penny, that can darken to look red, yellow or orange over time," says Nicolas Martin, flea market expert and founder of Flea Market Insiders. Brass, on the other hand, appears more yellow and tends to be much brighter. Look closely subtlety of tones in the item to see whether it is really copper or something else. You may need to polish the item first, especially if it appears dull.

The Magnet Test

Like silver and gold, real copper does not have much magnetism. "Just like real silver, copper is only very slightly magnetic," Martin says. "You can conduct the same magnet test by placing a magnet on the surface of the item. If the magnet sticks, you can make sure that the item isn't copper." Small magnets are also easy for you to bring to the flea market or antique shop. Even if an item is made from metal plated with real copper won't pass this test-the metal underneath will draw the magnet. An item that's made entirely of copper, on the other hand, will not attract the magnet.

The Oxidation Test

Copper corrodes in a very unique way. It does not rust. Instead, the oxidation process creates a crust that is blue or green in color. "There are many ways to check for real copper, but you probably won't have a lemon or a white light while shopping at the market," explains Sue Whitney, who has authored five books on antique shopping and decorating with repurposed furniture. "Copper found at flea or vintage markets will most likely be well patinated." Copper corrodes in a very unique way. It does not rust. "Oxidation on real copper presents as a crusty growth of blues and greens set upon a powdery red coating on the surface of the copper."

Conducive to Electricity

You'll want to be careful when testing this, but real copper is a great conductor of electrical current. To test the authenticity of your copper piece in this way, you will need a device called an ohmmeter that can measure the object's electrical resistance. You'll have to do some math next: take the reading from the ohmmeter and multiply by the cross-sectional area of the item, then divide that number by the length of the object. Real copper will have a resistivity of 1.7 x 10^-8 ohm-meters.

The Sound Test

Copper has a distinct sound to it. "Strike your copper item against something and listen to the sound," says Martin. Real copper is a soft metal and should deliver a deep and mellow sound, as opposed to alloys that are more likely to produce a clear, ringing bell-like sound." Other materials will produce different sounds. But real copper always sounds like copper.

The Smoothness Test

Martin suggests holding the item in your hands. "Does it feel really sturdy? Copper is notoriously soft, so it can be difficult to keep a piece perfectly smooth when working with the copper," he says. "If the copper piece is thin enough, you may even be able to bend it with your bare hands." Know the feel and texture of real copper when you go to the market. This small test can indicate whether you are holding the real deal or a decent copy.

The Density Test

Another test that involves math is the density test. Real copper is fairly dense, measuring at 8.96 g/cm3. Weigh the object, then divide by the object's volume to figure out its density. Is the density the same or very close to the density of copper? Then the object is made of copper. If the number is very different, the object might contain some copper, but is not pure copper.

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