Difference between red and brown copper toning?

Discussion in 'Coin Chat' started by mrjason71, Dec 5, 2017.

  1. mrjason71

    mrjason71 Active Member

    I've heard (read) you say that copper begins turning the moment it leaves the mint (or sooner). There are many shades it turns before being considered brown--red encompasses quite a few shades, no? From pink to orange...

    Did an experiment last night. Dropped a few cents in a plastic bag with a sulfur emanating substance. I can see it is definitely a gradual process. What is interesting is that the cents that were full red to begin with--those with full luster--tone much less slowly. Those places where luster were broken really toned fast and are brown over night. The toning is also very spotty. I'm thinking luster is what makes copper tone evenly. Or is luster tone? I believe that's the case. Fascinating stuff. You need even luster to get even color. All other things being equal. Thanks as always for considering my questions. Learning a great deal :)
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  3. Buddy Love

    Buddy Love New Member

    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.
    jafo50, mrjason71, tpsadler and 3 others like this.
  4. desertgem

    desertgem MODERATOR Senior Errer Collecktor Moderator

    The luster is from the microscopic flow lines from striking. However as you quoted above from Doug, The fresh copper surface begins reacting immediately to the environmental air. The press room is not like NASA, there are volatile substances in the air that starts to react with the surface in a thin layer. This thin layer on the coin surface offers protection as time progresses from other reactive substances, and produces a slow change in tone over time. If any scrape or rub in circulation or damage removes some of it, then the pure interior copper will be exposed and react. If someone has put it into a more contaminated environment ( toning experiment :) ) they will react with a different end product and produce colorations that are not normal for the rest of the coin surface. Jim
  5. SuperDave

    SuperDave Free the Cartwheels!

    Please don't make this your last post as well as your first. :)

    Understanding the chemistry behind coin interactions is the best way to avoid believing opinion based on things which are not fact.
    tpsadler, Kentucky and RonSanderson like this.
  6. Michael K

    Michael K Well-Known Member

    Did you drop copper cents in the bag 1981 and before, or copper plated zinc cents 1983- present?
  7. Colonialjohn

    Colonialjohn Active Member

    Buddy Love has the closest answer. Copper forms different oxides with various colors. We see more colors in older coppers and we see these different colors particularly in U.S. Colonial coins. I guess with longer time frames exposed to both sulfur and chlorine (chlorides) we have much more different colors on coppers than 20thC or even 19thC copper type coins. See Wikipedia on copper and its oxides - we see brown, black, green, orange and blue. Can't think of another at the moment ... different copper oxide compounds ... different colors ... not so much sulfur (copper sulfide) but mostly copper oxides.
    I discuss this briefly in my new Amazon Book "Forgotten Coins." Soon ... very soon.

    John Lorenzo
    United States
  8. Buddy Love

    Buddy Love New Member

    Copper oxide is black in color. There are two states of copper oxides, copper I oxide, orCu2O, and copper II oxide, or CuO. Copper oxide is not green, orange, or blue.

    GDJMSP Numismatist Moderator

    Yes, kinda. As others have said, copper isn't really red, but that is the word, the color, that is used to describe untoned copper. if you asked 100 different people (who do not know coins) what color untoned copper was you'd probably get at least 10 different answers as to what that color was.

    And that said, there are several different colors that are considered to be original mint red. What I mean by that is that not all copper is exactly the same shade of color when it is untoned. Most of it is quite similar in color but some can have a slight yellowish cast to it, a pinkish cast, a reddish cast, and an orangeish cast. But this is due to the coins coming from different batches of copper, or copper mined in different places.

    To be Red, the accepted definition is that the coin must be 95% or more original mint red. Now another way of putting that would be this - to be Red no more than 5% of the coin can be toned any other color other than original mint red - whatever shade that original mint red color happened to be. In other words toning is the factor that matters, the factor that determines if a coin is original mint red or not. Not the shade of the color that is being called red.

    You've hit upon a key point, that is that luster is what makes coin tone more quickly. This is because the what creates the luster is the metal being in flow lines. And the very top of those flow lines is quite fragile because the metal is so thin there - it's only a couple of molecules thick.

    Think of luster, the flow lines, as looking like this - /\/\/\/\/\/\/\ . It's a series of peaks and valleys and the very tip of the peak is the very fragile part. That is why it is so easy to destroy or break the luster with even minor contact - because it's only a few molecules thick there. And, toning has the same kind of effect because it's so thin there - it allows the air to affect it more readily, to corrode it more readily.

    This is also why we so seldom see circulated coins that have any color to them - well other than what we call battleship grey or with copper brown. It is because circulated coins don't have much if any luster left on them.

    Now if you really want to try an experiment take some unc cents, rub them with your finger or a cloth and destroy the luster. Then put them side by side, in the open air, with some unc cents that have their luster. And then watch the difference in how the 2 different kinds of coins tone. And if ya really want to mix it up, take some toned unc cents that still have their luster, dip them, and put them side by side with the other 2 kinds of coins.

    What you will see is that the original unc cents and the dipped unc cents both tone at about the same rate, while the coins you destroyed the luster on tone much more slowly than either of the other two. And all of this will occur in just a week or less.

    And if you don't think they've toned in that week, then dip just the bottom half of the coins and you'll quickly see just how much they have toned in that week !
  10. Kentucky

    Kentucky Supporter! Supporter

    Welcome to CT. Chemistry is really complicated stuff and as soon as I think I understand or have explained something, I get a "Yeah, but...". I have told kids in chemistry classes that metals are either silver, copper or gold, referring to colors rather than composition. Copper and gold can and have both been called "red" and some kinds of toning (corrosion if you wish) can give you these colors.
  11. Kentucky

    Kentucky Supporter! Supporter

    But copper sulfate is blue...
    Kirkuleez likes this.
  12. desertgem

    desertgem MODERATOR Senior Errer Collecktor Moderator

    In Visible light spectrum, yes. But only because it absorbs the other wavelengths and reflects the blue wavelength. If it was in a spectrum outside of the visible one, it would not. Trying to explain the scientific reasons why color is what they are can start with the simple, The material absorbs most colors and reflects the ones we actually can see. More complex theory delves into the quanta realm and explains why corundum ( aluminum oxide) can be red ( ruby) or yellow, blue, and various shade and mixes of those ( Sapphires), depending on what ions or color centers ( holes) are present. Color changing minerals on reacting to artificial light or sunlight depending on a energy level to cause a particular change. What color is a bright piece of amethyst in the dark? Same as a piece of crystal clear colorless quartz in the dark :)
  13. Buddy Love

    Buddy Love New Member

    Sorry, I am missing your point...
  14. Kentucky

    Kentucky Supporter! Supporter

    Actually it is blue in transmission as well as reflection. Take a look at a CuSO4 solution...
  15. Kentucky

    Kentucky Supporter! Supporter

    You were mentioning the colors of the oxides of copper, but I didn't want people to get the impression that all copper compounds are red or black.
  16. Buddy Love

    Buddy Love New Member

    Yes, agree completely. I was responding to MrJason's question about red on copper, and also responding to Colonialjohn's misinformation that the copper oxide compound creates multiple colors. It does not.

    The OP wondered about the interaction of red and brown colors with other colors on copper coins. I was also trying to respond to that comment. I think there is a general mistrust or, moreover, general lack of understanding in the collecting community of colorfully toned copper coins. More knowledge and understanding is needed on how copper coins can tone naturally into either a rainbow of colors, or monochromatic colors.

    Copper sulfides combined with copper oxides are the primary cause of rainbow colors, and much of that can be explained by oxide and sulfide thin interference films.

    I agree that chemistry is complicated stuff. Suffice to say, though, that copper compounds can cause copper to take on vibrant natural colors, especially blues and greens, and in monochromatic form. That is to say, copper coins don't necessarily naturally turn just red and brown.
  17. GDJMSP

    GDJMSP Numismatist Moderator

    And nobody was trying to say that they do only that.

    You just got here yesterday and what you have to understand is that this thread is merely an extension of a discussion in several other recent threads that has been ongoing for some time now. And since the title of this thread is - Difference between red and brown copper toning? - that is what was being discussed in this thread because it applies to the other threads.

    Regarding the chemistry of toning, that could be discussed for weeks but the average person isn't going to understand it - nor would it even matter to them. What the average person cares about, and I'm including some pretty advanced collectors in that group, is what they can see, what they can discuss and understand in laymen's terms. Talking about the chemistry of toning to most collectors, well you might as well be discussing particle physics because all it does is confuse the situation - not make it better.

    That said I certainly have no problem with the discussion of it, but in the end how much good is it going to do ? The vast majority of collectors don't care if it's oxides, or sulfides, or sulfates, or or or that make the coins the color they see. What they care about is the color they see - and whether they like it or not. And, the basics of how it got that way - the basics of the toning process in other words.
    352sdeer likes this.
  18. Buddy Love

    Buddy Love New Member

    Because that was the question the original poster posed, and I was trying to answer his question. He asked for a scientific explanation of toning on copper coins, and it is not the point whether you care to hear the answer or not. Let MrJason respond as to whether this sharing of information was helpful to him. What I provided was a basics of the science of toning, as you suggest conversations should be, and my apologies if it was too complicated for you.

    The more knowledge and understanding a collector has about his collecting interests, the better collector they will be. That is especially true for collectors of toned coins, as it helps them identify naturally toned coins versus those that are not. If you are telling me that the folks here on this board don't want or need this type of information, I can leave here as quickly as I came.
  19. Kentucky

    Kentucky Supporter! Supporter

    [QUOTE="Buddy Love, post: 2928564, member: 91504...If you are telling me that the folks here on this board don't want or need this type of information, I can leave here as quickly as I came.[/QUOTE]
    Why not hang around and read some before educating us.
  20. Cheech9712

    Cheech9712 Every thing is a guess

    Im believing you
  21. Cheech9712

    Cheech9712 Every thing is a guess

    I still like your answer best. I get it
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