[Jewelry making - Article 00338] - Re: [Orchid] Article: Minimal Metalsmithing

[leonid surpin]

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>     No matter what you think of fabricating items in PMC, there is no
>     reason it is not as acceptable a medium for making your metal
>     master for casting as wax. 

    There is precisely the case where PMC should not be used. 

    There was a thread dealing in porosity in casting. A lot of good
    advice was given on how to prevent porosity, but most of it was
    concentrated on casting, when the real reason most of the time is the
    badly design model. 

    In order for the casting to come out well, the designer must insure
    that metal entering the cavity would have laminar flow. Turbulence
    means porosity. To insure laminar flow the model must be constructed
    using metal working techniques. Then the natural properties of metal
    would insure laminar flow of liquid metal. 

    If you wondering about all the models made in wax you are correct.
    Wax is a tradeoff between ease of making a model but then spending
    some time fixing the porosity. There is no advantage in using PMC
    because it is not as easy as making wax model but have the same
    disadvantages as wax, and definitely more expensive. 

Leonid Surpin
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