[Jewelry making - Article 00111] - [Orchid] Opals & Glycerine.

[John Burgess]

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    G'day;    Opals;  about which I know very little.   But there's been
    a lot of 'talk' referring to glycerine, about which people don't seem
    to know much either.   Oh, they know vaguely that it is a constituent
    of most hand creams, and used with some opals but don't realize why.
    For a start pure glycerine is a highly refined by-product of the
    soap industry, and that thick, clear, treacly liquid is avid for
    water.  In fact, when it is diluted with water it gets quite warm. 

    So manufacturers put it in hand creams, lipsticks etc, to stop the
    products from drying up and to keep them soft and moist.   It is also
    used with cake icing to stop it  drying out and  hardening . So I
    assume that if one has opals which are at risk of demoisturizing and
    therefore distortion followed by crazing due to the missing volume
    previously occupied by water,  storage in a strong solution of
    glycerine would stop the evaporation of water held in the opal.   If
    the glycerine solution is very slowly changed over some weeks with
    increasingly stronger solutions, the water in opal would be entirely
    replaced by pure glycerine, which would not easily evaporate.     
    It is obviously the loss of water causing changes in the edges faster
    than any change near the centre which causes distortions and crazing.
    Thus, an opal which had contained water would not dry out.  But with
    temperature changes, the opal might 'sweat' glycerine. To test if the
    'sweat' is oil or glycerine, touch it with a finger, then taste it
    with the tip of the tongue.  Glycerine is very sweet.  And no, it
    isn't poisonous unless you guzzle huge amounts. 

    Scientists sometimes want to examine a tiny piece of plant or animal
    tissue, which would quickly dry out and distort.   So they first
    remove the water by placing the piece in a series of ethanol/water
    solutions of increasing alcohol content, until they end up in pure
    alcohol.  They then mount the dehydrated  tissue in something that
    will stop further changes; to keep out bacteria and fungus to
    preserve it permanently, and of course it must be compatible with
    alcohol. 

    I don't know if opals dehydrated by such a method would craze or not;
    but the dehydration would have to be performed very slowly, and then
    one would have to find something to finally replace the alcohol or
    glycerine it now contains.  P.E.G - poly ethylene glycol?  Want to
    experiment?  It is being used to slowly replace sea water in recovered
    sunken wooden ships. -- Cheers for now, John Burgess;   johnb AT ts.co.nz
    of Mapua, Nelson NZ  

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