[Jewelry making - Article 00077] - [Orchid] Flux

[John Burgess]

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    G'day;   I wrote something on these lines a few years ago in Orchid,
    but here we go again. again; Question:    why is borax a flux?   What
    actually does a flux do anyway? (same question) 

    A flux is a substance that cleans the surfaces of metals which are
    to be heated, and as a consequence of the heat, will combine with
    oxygen, sulphur, and other materials present in the atmosphere or
    metal. thus keeping the surface fresh and clean. Fluxes do this
    because they have a special affinity  for metallic oxides and other
    compounds. Borax  has such an affinity for metal oxides, etc,  and
    converts them into acid soluble borates which are iin fact glasses
    and can be washed off heated work and dissolved in acids such as
    sodium bisulphate, citric acid, 10% sulphuric acid and even lemon
    juice. after heating is finished. Borax is not the only material used
    as a flux.   Plumbers used to use tallow when  jointing lead for
    pipes and tanks.   Electronics technicians use a special resin as a
    flux for tin/lead solders, as any acid left after soldering could
    cause electrical faults. Borax used in some higher temperature work
    with uncompromising metals, often contain ammonium or sodium
    fluorides, which help with the dissolving of metal oxides.  Brazing,
    using brass alloy rods with some bronzes, iron, nickel, and so on
    work better with the presence of fluorides in the flux, and even
    silver and gold join more easily with fluoride fluxes.   But
    fluorides are poisonous, and care must be taken not to inhale the
    fumes.    But don't go overboard about fluorides;  just be careful,
    but remember that your natural teeth are coated with a fluoride
    complex.  (Heat a tooth with sulphuric acid and the resultant vapour
    will etch glass) 

    Now, given all this, what might one expect to happen if gemstones
    were to be coated with boric acid or borax and heated to red heat? 
    As you now know that boron compounds have an affinity for hot metal
    oxides and other metal compounds, you should expect it to etch
    gemstones like ruby, sapphire, tourmalines, agates, and so on..   I
    am well aware that some books reccommend this, but now you know why
    people like me say you should be careful to keep fluxes away from
    precious and semi precious stones. 

    In other times before instrumental chemistry became possible. one
    had to  get the unknown chemical into water solution to enable
    subsequent analysis, and this was accomplished by heating the
    unknown strongly with borax, then dissolving the result in
    aciidified water so that other reagents could react and provide
    clues as to what the unknown contained.  Any person over the age of
    50 will tell you this form of analysis was used to help teach
    chemistry in the sixth form. (Don't really know why they stopped that
    method of teaching) 

    Here endeth the lesson. 

-- 
Cheers for now,
John Burgess;   johnb AT ts.co.nz of Mapua, Nelson NZn fact, glasses,


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