[Jewelry making - Article 00072] - Re: [Orchid] Casting porosity

[LEESSILVER]

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    Hunter, Sounds like you have a bag of worms. 

    It might be helpful if you described you casting procedure in more
    detail. Vacuum or centrifugal casting?  What was the metal and mold
    temperature?  How long did you burn out and what type of wax were
    the models?  Carving wax requires a longer burn out.  What was your
    burn out temp? In general you description might indicate incomplete
    burn out which could be the cause of surface porosity and incomplete
    castings.  The mold should be pure white when it comes out of the
    burn out oven. 

    Incomplete castings could indicate that the metal/mold temperature
    was too cold.  For vacuum casting I use a metal temp of 1850 and a
    mold temp of 860 degrees.  That combination seems to work for all my
    big and small castings. The sticky silver might indicate the metal
    was not hot enough and was chilling on the surface of a cold stir
    rod.  There was a time in my early use of an electro melt furnace
    where the silver formed a thin layer of silver on the top of the
    crucible as I poured.  I found that the top part of the crucible was
    too cold and was chilling the silver as it poured.  I don't pour
    until about 5 minutes after the metal reaches 1850 degrees.  That
    allows the ring of the crucible to heat up. I would be very
    suspicious of the scrap silver you used.  That might account for the
    excessive slag.  Was the copper shot pure or an alloy?  You should
    try to remove the slag before you pour the metal.  Slag in the mold
    could cause poor castings. The ratio of new vs scrap silver should be
    at least 50-50.  I use 60 new and 40 old. That's my 2 cents Lee
    Epperson 


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