[Jewelry making - Article 00039] - Re: [Orchid] Ancient gold granulation process

[Manuel and Faith]

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    "Aside from the technical difficulties of making the physical bond
    between the grains and the metal sheet, the Etruscans used incredibly
    tiny granules (0.14mm as opposed to 2mm grains used by the Sumerians,
    1.1-0.4mm grains used by the Trojans and 0.25mm grains used by the
    Greeks). Some Etruscan jewels appear to be dusted with minute gold
    beads covering a substantial surface area or arranged in tidy
    patterns. Each granule maintains its own integrity; metal isn't
    welled up around it, yet it's fused securely to the metal underneath."(
    Granulation: reviving an ancient technique, Elise B. Misiorowski) 

    We are talking about granules no bigger than half a grain of sand and
    smaller.  Has anyone succeeded in using the eutectic process to bond
    such minute granules?  If so, kindly tell. It was this very fact that
    suggested to me(I'm not yet aware of others on the same line of
    thought, please be so kind as to give me some references) that the
    process may not have involved melting(i.e. reaching a eutectic melting
    point)  Would one even be able to discern any noticeable "flash" of
    flowing eutectic between these miniscule granules.  To control a torch
    flame in such a way as to remain below puddling point of these
    granules I imagine would be difficult.  Whether it be copper alloy or
    gold carbide any near melting temperatures would seem to pose a
    daunting challenge for the success of granulating such small
    components. As far as making the small granules it was suggested that
    this might be difficult in an age that didn't have draw plates.  A
    plausible technique was the use of gold shavings(as opposed to our
    jump rings or pallions) layerd in the charcoal.  But let me run
    another possibility by you all.  Brennan got me looking up powder
    metallurgy and in this modern process there are quite a few techniques
    for creating metal powder, size of grain completely controllable. 
    Only one stuck out as being an available possibility for the Etruscan
    masters.  In PM they pour the molten metal through an orifice at a
    controlled rate and in turn this stream is subjected to a controlled
    jet of gas or air in effect "spraying" the metal.  A cruder form of
    this could have one etruscan pouring a "steady" stream of molten gold
    from a crucible and another with a blowpipe providing the "steady"
    gust to separate the stream into small particles(over a basin of water
    maybe).  Likely it would involve some sorting.  Dave's "Indian jewelry
    with extremely  tiny, medium and large gold granulation" suggests a
    very decorative sorting. :-) As far as the idea of diffusion and
    pressure mentioned in the Tribute to the Etruscan post.  I hadn't
    figured that the encasing in clay ( brennan suggested addition of
    dung) would be limited to flat pieces.  In powder metallurgy the
    powder is bonded under some 50-100lbs/sq.in. at diffusion
    temperatures, though I think that this may be overkill for the
    aspirations of a goldsmith.  How much pressure would the clay exert on
    the expanding metal within before the clay cracks?  we won't know
    until one of you tries it or until I finish making my furnace.  One
    thing we do know is that with diffusion a lower temperature only slows
    down the process so there is no need to fret over having to keep the
    clay from cracking at the "speedy temperatures.  The very articles
    made by the Etruscans suggest that these craftsman were already very
    familiar with the virtue of patience:) 

Manuel
Ad Meiorum Dei Gloriam





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