[Jewelry making - Article 00226] - Re: [Orchid] The Beilby Layer

[nick]

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    A Beilby layer is a thin layer of amorphous material, usually about
    15 nanometres thick on the surface of a polished material. It is
    caused by the displacement of the atoms (dislocation) during
    polishing, whether mechanical or chemical or by ion bombardment.
    Essentially, this layer has lost its normal atomic structure. It
    gives rise to problems with characterisation of many of the new
    materials used in making the next generation of semiconductors and
    the like which are grown epitaxially on a particular crystal
    orientation of a substrate. In the polishing of metal for a super
    high shine finish it is a plus because it hides the small differences
    in reflectance of the different parts of an alloy. Try making a
    copper/silver alloy from a molten state and cool it slowly. You will
    get separate dendritic grain growth of the silver and copper metals
    and when you polish this will be visible. Repickle the piece of metal
    and polish it with a lot of pressure. the surface will then smear and
    flow slightly. The visible result of this is a brigher and even
    surface. Electropolish (bomb) the surface and it will show its
    crystal grains again because the Beilby layer has been removed. 

Nick
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