Author Topic: How to tell brass from bronze  (Read 5263 times)

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Offline cannonmn

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How to tell brass from bronze
« on: November 04, 2007, 05:48:38 am »
I'm seriously interested in being able to know how to detect brass vs. bronze since I run into it all the time on the Ebay antiques discussion boards.  I'm one of the people who answers questions about pictures of items people post there (voluntary thing.)  The brass vs. bronze question comes up a couple times a week minimum.   No one there including myself has found a sure-fire way to do it from pictures, and it is pretty hard in person too.

Some clues would help me.

My apologies to the poster here, don't mean to hijack his discussion.

Graybeard Outdoors

How to tell brass from bronze
« on: November 04, 2007, 05:48:38 am »
 

Offline Tropico

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Re: How to tell brass from bronze
« Reply #1 on: November 04, 2007, 01:04:21 pm »
I always found it to be pretty easy to tell the difference when its in front of me., (visually speaking) . Brass is yellow and Bronze is red . its real obvious when there side by side and after seeing enough of it., you can pik it right out. Bronze has a high copper content (Usually at least 85%)  . 

On ebay or thru a photo however your pretty mush at the mercy of someone else's word.
Also for the most part bronze indoor will brown and darken almost blacken. Outdoor it will patina green  I haven't seen brass do either...,well a little green I suppose in spots..,especially inwet areas.., (threads ect.,)  Ive just seen it get to a dull then flat yellow.


Offline GGaskill

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Re: How to tell brass from bronze
« Reply #2 on: November 04, 2007, 10:46:02 pm »
In modern copper alloy parlance, brasses have zinc as the major alloying element and bronzes do not.  Thus an alloy of 94% Cu and 6% Si is called silicon bronze even though it has no tin, which used to be the element defining a bronze.  Civil War and older bronzes were typically 10% Sn and 90% Cu, give or take trace elements.

I think it would be virtually impossible to determine brass from bronze via photograph.  eBay is a  counterfeiters dream.  Even with a piece in hand, I think you would have to resort to chemistry to have a definitive answer.
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Offline cannonmn

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Re: How to tell brass from bronze
« Reply #3 on: November 04, 2007, 11:40:40 pm »
Quote
I think it would be virtually impossible to determine brass from bronze via photograph.  eBay is a  counterfeiters dream.  Even with a piece in hand, I think you would have to resort to chemistry to have a definitive answer.

I've kind of been thinking along those lines.  A few pointers I give to folks who ask, is to consider whether the object at hand is typically made of one alloy or the other, for a reason.  Fine statuary is made of bronze to pick up fine detail since art bronze expands slightly in the mold before it sets.  Ordinary household wallplates for light switches would normally be made of brass because bronze isn't required for that function.

Gunmetal bronze is very hard stuff, much harder than brass.  I tried to stamp some small letters in it one time and had to strike the metal stamp over and over.

If you ever really, really have to know and there's money at stake, take the item to a scrap dealer.  These days they are all equipped with a "gun" that is a handheld spectral analyzer.  it zaps the sample with an intense spark that vaporizes a tiny patch of metal then instantly decodes the spectrum of light emitted, and gives a printout of the top 20 elements and their percentages.  The spot chosen to zap has to be completely cleaned of all oxide etc. or all the components of that will contaminate the results.  If you know the scrap dealer he might do it as a favor, otherwise they may want to charge you something, or they may not want to do it at all unless you are doing other business with them.

Not all of the guns will ID all of the elements.  I wanted to buy some zinc recently and a dealer told me he had no way to tell it from lead or whatever since his zapper was not programmed to identify zinc.  That seems strange since it will identify brass vs. bronze, so I suspect he was giving me a line of b.s.

 

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