[Jewelry making - Article 01075] - Re: [Orchid] Curing investment under pressure for casting

[Peter W . Rowe]

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>     i suppose some sort of control experiment to determine & compare
>     the ratio of weight to volume would settle this claim

    Or, just remember your old physics classes. Water is not
    elastic/compressable, and neither would be the particles of silica or
    other minerals making up the investment powder. So pressure won't
    compress either one. The mix of the two forms a slurry, or emulsion,
    and the end density of the investment would depend on how much water
    is spacing those particles apart when they bond to each other, as
    well as the degree to which, before it sets up, the particles settle
    out, leaving liquid water on top. I can think of no reason why air
    pressure would increase that settling rate, especially given the
    speed with which most investments set up. So if it doesn't settle out
    more, and we already know the volume of water doesn't change with
    pressure, then the volume of the set investment would remain the
    same, and thus the density wouldn't change. 

Peter
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