[Jewelry making - Article 00231] - Re: [Orchid] Heat patina on copper

[Michael Honeycutt]

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    Hi Stephanie, A lot of what's happening on your copper may indeed be
    due to a lack of proper heat. When you heat copper and get beautiful
    colors it is just a heat-accelerated form of oxidation forming on
    the surface. I have honestly never tried heating copper with a heat
    gun but I suspect insufficient heat may be the culprit. I've also
    never run across copper colors from heat that disappeared when they
    were touched. But there are many things in this world that I don't
    know about. 

    I have worked with quite a bit of copper in the form of sculptures
    and the like though, so I can tell you a few things. 

    Like I said earlier, heat colors on copper are a type of oxidation.
    Touching the surfaces of copper will leave traces of oil/sweat from
    your fingers and, while the results are not immediately noticable,
    given a couple of days ( especially if it's highly polished) you'll
    be able to see clearly where it was touched. Big ol' fingerprints
    and smudges that definitely will change the colors where they are
    found. If not covered with some type of surface protectant those
    colors will rapidly fade to gradually deepening shades of brown.
    Even if you never touched them those colors are temporary at best.
    I've tried covering my colors with clear spray paint (both enamel
    and acrylic), clear lacquer, polyurethane spray...... all with the
    same result, the copper colors that were so beautiful went away.
    Something about a coating destroys the effect. Personally I believe
    that the surface of the copper, when heated for color, is affected
    on a molecular level on the very surface where the oxide is growing.
    This surface manipulation of oxides causes the light that is
    reflected off the surface to appear to be different colors due to
    differing spectrums of light being reflected. Thicker oxides reflect
    different colors than thinner oxides. A coating on the surface over
    the oxides thoroughly changes things in that chemical reactions on
    the surface will change the nature of the oxides chemically.
    Coatings also will reflect their own characteristics, cover the
    colors and change the way light reflects off the oxides. Gums the
    colors right up. 

    I have yet to find a suitable coating that would protect the
    beautiful colors. 

    There are some posibilities you might try for a heat source though.
    I've used the kitchen stove. Ours is gas and requires lots of
    practice to get good results. I don't see why heat from an electric
    range couldn't be utilized as well. They certainly produce plenty of
    heat. A simple electric hotplate might do the job. 

    I would recommend trying chemical manipulation to achieve varying
    color effects. Liver of sulfur, gun bluing, different types of acids
    all might work. 

    Sorry I couldn't really help you out. I've struggled long and hard
    to maintain colors on copper with only very limited success. 

Mike

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