Why would a 1939 Lincon Cent be 93% Cu, 5.5% Zn and 1.5% Sn?

RKKay · March 28, 2008 8:14AM

...when bronze is usually 95% Cu, 4% Sn and 1% Zn? Any ideas?

coolest · March 28, 2008 8:46AM

Where are your values coming from? An actual metals assay will have some degree of variability.

Lakesammman · March 28, 2008 9:49AM

It's like chocolate chip cookies - no matter how much you mix the bowl, some cookies have more chips than others.

MrEureka · March 28, 2008 10:10AM

The test only reads so far into the coin, which is another reason why it's not completely reliable.

RKKay · March 28, 2008 2:14PM

<< The test only reads so far into the coin, which is another reason why it's not completely reliable. >>

But the alloy should be relatively consistent in 1939. As well, there's no way SEM-EDX tests would have this degree of variability.

RKKay · March 28, 2008 2:15PM

<< Where are your values coming from? An actual metals assay will have some degree of variability. >>

The numbers were acquired via SEM-EDX testing.

BAJJERFAN · March 28, 2008 2:19PM

<< ...when bronze is usually 95% Cu, 4% Sn and 1% Zn? Any ideas? >>

Perhaps that batch of metal was mixed differently for some reason.

BAJJERFAN · March 28, 2008 2:22PM

<< It's like chocolate chip cookies - no matter how much you mix the bowl, some cookies have more chips than others.

>>

Except here the metals are melted together so the composition should be uniform throughout the melt, UNLESS you are willing to believe that a cup of salt water has more salt near the top than it does neat the bottom.

RKKay · March 28, 2008 2:29PM

<< 

<< ...when bronze is usually 95% Cu, 4% Sn and 1% Zn? Any ideas? >>

Perhaps that batch of metal was mixed differently for some reason. >>

Makes sense, but it's a weird change to make.

Dabigkahuna · March 28, 2008 2:30PM

I don'y know about back then but the US Mint considers bronze to be 90% Cu and 10% Zn.

BAJJERFAN · March 28, 2008 2:42PM

<< 

<< 

<< ...when bronze is usually 95% Cu, 4% Sn and 1% Zn? Any ideas? >>

Perhaps that batch of metal was mixed differently for some reason. >>

Makes sense, but it's a weird change to make. >>

Maybe someone simply screwed up and there was neither time nor resources to fix it.

RKKay · March 28, 2008 3:05PM

I'm at a loss. I'm going to bed. Thanks for the feedback.

ProofArtworkonCircs · March 28, 2008 3:21PM

For most of the time up to 1958, the legal definition was .950 copper and .050 tin and zinc. As tin was expensive, the mint was using .005 tin and .045 zinc at the end.

CaptHenway · March 29, 2008 1:37AM

<< ...when bronze is usually 95% Cu, 4% Sn and 1% Zn? Any ideas? >>

For openers, you should have explained what the heck you were talking about before asking a question about it.

Many coins are not completely homogeanous. Look at the many gold coins with copper spots on them. Do an X-ray test on the spot, and you will get a copper value much higher than 10%. However, the coin overall will be close enough to 90/10 as to be statistically right on. Take a nice brass-streaked 1909 cent and you can get all kinds of ratios as you move accross the surface. However, melt the coin down to a blob and remix it and you should get very close to 95/4/1.

TD

Why would a 1939 Lincon Cent be 93% Cu, 5.5% Zn and 1.5% Sn?

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