[Jewelry making - Article 00201] - Re: [Orchid] The Beilby Layer

[Wayne Emery]

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Helen,

    The Beilby flow explanation for polishing was discredited long ago,
    and no one accepts it today. it implied that with the use of certain
    oxides, some mineral material get hot enough locally to allow the
    layer to flow, thus creating a polish. Doesn't happen, can't happen. 

    HOWEVER, it is known that plastic deformation can and does take
    place during polishing of certain stones with certain oxides, but
    heat is not involved. It is a complex mechanical action involving
    shear limits and plasticity of the material. 

    Examination of surfaces with a scanning electron microscope formerly
    believed to be polished by the Beilby principle show the tell-tale
    minute scratches of conventional abrasive polishing. This subject
    usually comes up in connection wth cerium oxide and the quartz or
    beryl family. Cerium oxide breaks down rapidly in size under
    pressure and the polish that results is indeed exceptionally
    fine...but it is an abraded surface not a flow layer. Beilby flow
    does not exist. 

Wayne Emery
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