[Jewelry making - Article 00939] - Re: [Orchid] Magnesia soldering block

[jesse brennan]

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    Your "magneia block"supplier is selling sometying other than what
    the term  applies to. 

    "Magnesia " would  indicate magnesium oxide  a very high temperature
    refractory melting at 2800 C. They are used as a high temperature
    facing refractory in steel making. They  stand up to heat but have a
    high thermal conductivity and are not "insulating'. True magnesia
    blocks  would not have a binder and would not melt easily. You are
    obviously being sold some fibre or powder based material with an
    organic binder.  Maybe fiberfrax or kaowool board.  These would be
    good to about 1200  C. They would also be eaten into  by  borax type
    fluxes.  They will usually have  some organic binder that will burn
    off on first  heating. 

    In the case of 'silversmiths bricks'. They're 2 1/2" x 4 1/2" x 9" &
    weigh 1# 14 oz. 

    They're soft enough that pins can be pushed in with your fingers.
    These  would usualy be called "insulating firebrick" and  would be
    easiest to find at a ceramics supply house. Using  the term
    "silversmiths brick would probably bring a glazed look from most
    suppliers.  They are very lightweight - you don't want  the
    hardsurface  refractory firebrick. 

jesse


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