[Jewelry making - Article 00141] - Re: [Orchid] Verifying Gold Alloys - specific gravity

[Jack]

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    Specific gravity is a good guide to gold purity, but not that
    accurate for modern alloys. The specific gravity will vary with
    composition (ie the nature of the alloying metals which today can be
    v. diverse,) and mode of manufacture ('stamped' objects are more
    compact and thus have higher SG than some types of casting). So SG is
    only accurate if you know the composition, in which case you don't
    need to do the SG ... 

    Archimedes had simpler alloys to contend with - Iron Age gold
    objects are characteristically gold plus silver, rarely more than 2%
    copper. Prospectors and mineral hounds can take comfort in the
    thought that much the same is true with gold nuggest, 'cos those are
    usually just gold plus silver, rarely much more than 1 - 2 % copper. 

    Other testing techniques include that good old standby the
    touchstone and acid (still available in nice little boxed sets from
    suppliers). But again modern alloy types make this problematic - some
    commercial red karat gold alloys, for example, contain enough copper
    for them to froth up green and be mistaken for brass. AND, pet
    bandwagon, any jeweller who files a flat on a decent piece of
    jewellery and dabs a acid onto it should have the same acid inserted
    into each ear. I've even seen folk do that to antique jewlelery
    aghhhh. 

    That other modern jeweller's stanbdby, the electronic gold tester,
    can produce varied results and the general view seems to be that they
    are not that reliable. Any feed back on this area would be great. 

Jack Ogden

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