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Opals & Glycerine


#1

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; @John_Burgess2
of Mapua, Nelson NZ