[Jewelry making - Article 00411] - Re: [Orchid] Diamond cutting

[Peter W . Rowe]

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>        The old miners (fat and squarish) where cut to keep most of the
>     original octahedron intact and not loose weight.  Cleaving allowed
>     the yeilding of two stones from an octahedron. One larger and one
>     smaller (table to table in the rough) yeilding stones that could
>     be polished more to their "ideal proportions". 

A small correction, Mark.

    The above cut is along a cubic crystal plane, not the octahedral
    ones.  The latter are the directions in which a diamond will cleave,
    while the former are the softest directions, easiest to saw.  One of
    the key developments in diamond cut evolution was the development of
    the diamond saw, which allowed exactly the above seperation to be
    made.  Prior to this, an octahedral crystal yielded one old mine or
    old european cut stone. With the diamond saw, the crystal becomes two
    pieces, and two stones. Suddenly, too, the economics of weight
    retention mean that no longer is the high crown and small table the
    best for yield, but rather, the shallow crown and wide table of the
    "spread" stones.  So in addition to giving us more ways to divide a
    rough into multiple pieces, the saw also gave us spread and swindled
    stones...  Cleaving doesn't follow the needed directions to do this
    for uniform octahedral crystals. Mishapen ones, or those with flaws
    that require the stone to be divided, may be cleaved, and the
    cleavage planes that result may or may not be oriented near to the
    table facet.  Generally not exactly in the same plane, though, since
    the cleavage plane is also the hardest direction in diamond, and
    thus very difficult to polish. 

cheers
Peter

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