[Jewelry making - Article 00598] - Re: [Orchid] Article: Minimal Metalsmithing

[Mary Ellin D'Agostino]

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    Whew! What an interesting, if acrimonious thread. I just want to add
    a bit of technical information to correct some of the mis-statements
    made earlier. Some of this repeats corrections others have made, but
    with a little more detail. 

    It would be more accurate to state that Tim McCreight has claimed
    that fully sintered PMC3 *approaches* the strength of cast fine
    silver. I do not believe he has ever claimed it is the same as cast
    silver. His (or the PMC Guild's) published technical data on the
    product is available at

    http://www.pmcguild.com/gettingstarted/technicaldata.html

    Alas, no such similar information is published online for Art Clay 

    In particular, I would like to point out the tensile strength
    comparisons of PMC brand metals to fine and sterling silver
    published by the PMC Guild. 

    
http://pmcguild.com/download/Tech_Data/Tensile_Strength_Comparisons.pdf

    Tensile Strength:
    PMC Standard: 63 MPa
    PMC+: 116 MPa
    PMC3: 135 MPa
    Fine Silver: 157 MPa
    Sterling Silver: 311 MPa

    I assume the fine and sterling silver values are for cast rather
    than rolled metal. These numbers refer to fully sintered PMC fired
    for the maximum time and temperature. 

    Density information on the 3 types of PMC clay are available at 

    http://pmcguild.com/download/Tech_Data/Comparison_Summary_Sheet.pdf

    There is a lot more info on this page, but in short, it states that
    PMC3 clay (the strongest of the PMC brand clays) is 90% silver by
    weight with an unfired density of 5.5 grams/cubic cm. It shrinks
    10-15% when fired. When fired at the maximum schedule of 2 hours at
    900C (1650F), the density is 9.9 grams/cubic cm. Fine silver has a
    theoretical density of 10.5 grams/cubic cm. 

    There are some nifty pictures of the crystalline structure of fired
    PMC taken with a scanning electron microscope by Tina Carvalho. Fired
    metal clay definitely has a crystalline structure, though obviously
    not as dense as cast and rolled silver. Volume 10(1) of Studio PMC
    has additional information on the characteristics of both brands of
    metal clay. 

    I admit I am puzzled by Mr. Rourke's claim that silver clays are not
    pure metal and that no traditional metalsmithing techniques can be
    applied to it. What I am especially puzzled by his statement that it
    can't be "remelted." Perhaps I am reading this wrong, but I take this
    to mean that Mr. Rourke believes that you can't melt silver clay,
    pour it into an ingot and then turn it into sheet or wire. Having
    done this with more than a few of my rejects, I can assure you that
    it melts just fine and can be used to create perfectly good sheet and
    wire. 

    I use both metal clays and traditional fabrication techniques as
    appropriate in my work. 

    As for Ms Nanz job situation, we really don't know what happened
    there. The statement that she is no longer with the magazine has any
    number of interpretations. It is unfortunate that she didn't include
    one of those disclaimer statements about the views expressed not
    representing the magazine. 

Mary Ellin D'Agostino, PhD
www.medacreations.com
Sr. Teacher, PMC Connection
Certified Artisan, PMC Guild

 
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