Posted 03/22/2019 9:00 pm
Your question made me curious so I did some looking. I found this interesting article:
Quote:
Gold coins (and even pure gold bars) can sometimes develop brown (rust colored spots) on them. Yes, a gold plated item (when the gold plating wears off) would expose the non-gold metal underneath and that exposed metal could tarnish or rust. However, a brown or reddish spot on gold doesn't mean the item is not real solid gold. Here's why:
Rust spots or brown spots can occur on genuine gold coins when a very faint trace of other metal adheres to the surface of the coin or bar. As the other metal is exposed to oxygen or other materials in the surrounding air (can even be the air that is in the holder) it causes that trace metal to change color.
Often the a faint amount of trace metal or other material will get on the dies prior to the striking of the coin or bar. When the coin is struck the molecules of the other metal (or impurities) are then fixed into the coin. They may be so thin or dispersed that they are not obvious to the naked eye.
Other times such impurities may come in contact with the coin blank before striking it into a coin.. This surface discoloration can occur on gold coins and gold bars.
Most gold coins are between 90 to 92% pure gold depending on the country of issuance. Copper or silver are added to the gold during the melting process to give the finished solid gold coin a hardness. Although during melting the metal molecules are usually mixed well, sometimes traces of copper or silver will be collect near the surface, thereby allowing the change in color in that particular spot.
Gold coins (and even pure gold bars) can sometimes develop brown (rust colored spots) on them. Yes, a gold plated item (when the gold plating wears off) would expose the non-gold metal underneath and that exposed metal could tarnish or rust. However, a brown or reddish spot on gold doesn't mean the item is not real solid gold. Here's why:
Rust spots or brown spots can occur on genuine gold coins when a very faint trace of other metal adheres to the surface of the coin or bar. As the other metal is exposed to oxygen or other materials in the surrounding air (can even be the air that is in the holder) it causes that trace metal to change color.
Often the a faint amount of trace metal or other material will get on the dies prior to the striking of the coin or bar. When the coin is struck the molecules of the other metal (or impurities) are then fixed into the coin. They may be so thin or dispersed that they are not obvious to the naked eye.
Other times such impurities may come in contact with the coin blank before striking it into a coin.. This surface discoloration can occur on gold coins and gold bars.
Most gold coins are between 90 to 92% pure gold depending on the country of issuance. Copper or silver are added to the gold during the melting process to give the finished solid gold coin a hardness. Although during melting the metal molecules are usually mixed well, sometimes traces of copper or silver will be collect near the surface, thereby allowing the change in color in that particular spot.
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