[Jewelry making - Article 01062] - Re: [Orchid] Boric Acid vs. Borax

[Peter W . Rowe]

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>        I have always used  boric acid + alcohol  as a fire coat. Borax
>     is a different material isn't it?  I only use borax to cure
>     crucibles before melting...a very glassy coating.

    Borax and Boric acid are indeed different materials.  But they are
    related, and both contain boron.  In use, borax melts, and becomes
    active as a flux (dissolving oxides) at a lower temperature than does
    boric acid, so  it will etch rubies or sapphires more aggressively,
    and at a lower temperature. 

>        My concern, from reading on this forum, borax can be the cause
>     of damage to some sapphires and rubies by etching the surface. 

    Indeed it can.  borax, boric acid, and any of the soldering fluxes
    that I can think of, can all damage ruby or sapphire in this way. 
    But they won't do it all at the same rate.  Borax is worse than boric
    acid, and some of the highly active paste fluxes are even worse than
    just borax.  

    I too, use boric acid powder in alcohol to coat goldwork prior to
    heating, as a fire coat.  If working very near (as in retipping) a
    sapphire or ruby, I try to remove as much of the boric acid as I can,
    but generally, there will still be traces.  Usually you can get away
    with this if you're careful not to direct the flame actually at the
    stone, but just at the metal, so the stone remains at a low enough
    temperature that the traces of boric acid don't start to etch
    noticeably.  But if you actually get the stone glowing, then the
    chances of damage are much greater even with just boric acid, not
    flux or borax.   It's also quite dependent on how long it's at those
    temps. 

Peter


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