[Jewelry making - Article 00022] - [Orchid] Charcoal block soldering hearth

[John Burgess]

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    G'day   The way a charcoal (carbon) block works as a help to avoid
    firestain is that when the block is strongly heated with a flame to
    solder carat gold or sterling silver, a reaction begins between the
    carbon and the oxygen in the air, to form a mixture of carbon
    dioxide and carbon monoxide gases.   It is the carbon monoxide gas
    which stops the copper which is alloyed with the metal from
    oxidizing to black copper oxide, which is the dreaded firestain. 

    At the same time some of the charcoal will of course burn away and
    disappear.   Graphite slabs work as well, but tend to conduct heat
    far mor easily than porous charcoal, so a hotter flame is needed. 

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



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