Ask A Scientist Chemistry Archive

name         Monique M.
status       other
age          30s

Question -   What deficiency in a human body causes the skin to turn
black when it is rubbed with 14 Karat gold?
Everyone thinks my wedding ring is fake!  Help!
Some days my fingers are not black-makes me think it is something I am
eating or not eating....
I did check with Dels Jewelry. It is 14 k stamped on inside of ring
should I challenge their quality?
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I have heard this complaint several times, and I am not sure of the answer.
14 carat gold is an alloy of gold(~58%), copper(~14 - ~28%) and silver(~4 -
~28%). I doubt the black "rub off" is a metabolic deficiency, but rather the
abrasion of finely divided particles of the metal from the ring, that could
be ground off if you use abrasive cleansers, such as are used for cleaning
sinks or showers. Whether your finger is black depends upon what you have
been handling on that particular day. Keep a careful log of all dermal
contacts you have and see if you can find some correlation between the "rub
off" and materials you handled on a given day.

Vince Calder
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You may find the discussion on this website of interest:

http://www.24carat.co.uk/hardnessofgoldalloys.html

Vince Calder
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Monique,

Your ring is not a fake. However, a 14 K gold ring is not pure gold. Your
ring is 58 % gold; the rest is copper. Copper oxide is black. Some people's
skin chemistry can react with the copper in the ring to cause the skin to
appear greenish or black. So as you can see, there is nothing in your diet
that is causing the effect you see on your skin.

BTW, rings are rarely made of pure (24K) gold because the metal is too soft.
Most wedding ring gold is either 10K, 14K, or 18K. Some imported (and much
more costly jewelry) is as much as 22K. My wedding ring is a mere 10K --
only 42% gold. Nevertheless, it could not mean more to me if it were made of
purest platinum.

Regards,
ProfHoff 368
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