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Difference between red and brown copper toning?
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<p>[QUOTE="Buddy Love, post: 2927432, member: 91504"]My first post on Coin Talk.</p><p><br /></p><p>MrJason, you are on the right track here. Bare copper is not red, and an "original red copper coin" is a complete misnomer. Bare copper is salmon, light pinkish orange, however you want to describe it, not red.</p><p><br /></p><p>Copper oxidizes. Actually, copper oxide is black in color. There are two states of copper oxides, copper I oxide, orCu2O, and copper II oxide, or CuO. Copper first oxidizes to form oxide I, which is a red color (refer to pink oxide cuprite). This oxidizes further into II, which is a black oxide (refer to tenorite). It is this combination or further oxidation that can cause a red coin to turn brown.</p><p><br /></p><p>Some copper coins do not just turn red then brown, but take on other colors. This is a result of other interactions with the environment. For one, the presence of moisture and sulfides, along with other things including oxides, can produce a thin film interference on copper coins. It is the same effect you see on silver coins, but with a different starting color of the base metal. Not to get into a big explanation of thin film interference, but the first order of interference drops out other wavelength colors, leaving red as the dominant color. This is why you sometimes see copper coins that have built a thin film beyond the first order start to take on different colors. Blue tones are next, which explains some reddish/bluish/purplish looking coins, then yellows, reds, greens, etc. etc. through thin film build-up until a coin ultimately goes dark, or brown.[/QUOTE]</p><p><br /></p>
[QUOTE="Buddy Love, post: 2927432, member: 91504"]My first post on Coin Talk. MrJason, you are on the right track here. Bare copper is not red, and an "original red copper coin" is a complete misnomer. Bare copper is salmon, light pinkish orange, however you want to describe it, not red. Copper oxidizes. Actually, copper oxide is black in color. There are two states of copper oxides, copper I oxide, orCu2O, and copper II oxide, or CuO. Copper first oxidizes to form oxide I, which is a red color (refer to pink oxide cuprite). This oxidizes further into II, which is a black oxide (refer to tenorite). It is this combination or further oxidation that can cause a red coin to turn brown. Some copper coins do not just turn red then brown, but take on other colors. This is a result of other interactions with the environment. For one, the presence of moisture and sulfides, along with other things including oxides, can produce a thin film interference on copper coins. It is the same effect you see on silver coins, but with a different starting color of the base metal. Not to get into a big explanation of thin film interference, but the first order of interference drops out other wavelength colors, leaving red as the dominant color. This is why you sometimes see copper coins that have built a thin film beyond the first order start to take on different colors. Blue tones are next, which explains some reddish/bluish/purplish looking coins, then yellows, reds, greens, etc. etc. through thin film build-up until a coin ultimately goes dark, or brown.[/QUOTE]
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Difference between red and brown copper toning?
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