[Jewelry making - Article 00544] - [Orchid] Investment cracking.

[hoods]

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    The posting from jagman425 AT aol.com was right on. I've been casting
    for about thirteen years now and have had a recurring problem with
    breakouts and cracking. I've gotten lots of advice on the subject and
    have read several casting manuals looking for a solution. Many
    included too much water as the problem but nobody ever mentioned too
    little water. 

    Many years ago I met a goldsmith at a Jewelers Convention in
    Newfoundland. He said he always mixed by "feel" and said to mix the
    investment to the consistency of sour cream. I know now that that
    would make the investment short on water. In the last few months I
    have been mixing my investment and very carfully measuring the
    ingredients. I use a very large injection needle to measure the
    water. The result has been perfect castings every time. The mixed
    investment has the consistency of whipping cream (unwhipped). 

    I think that books on casting place too much emphasis on what can go
    wrong with your investment. They should simply say measure the
    ingrediants exactly to the manufacturer's specs. and if you have
    problems, calibrate your measurement equipment. If you still have
    problems, then you can rule out improper mixing of the investment and
    look somnewhere else. 

    Now that I am more confident I have gone back to my investment scale
    and use a pyrex beaker for measuring the water. I use the hypodermic
    needle to fill exactly between graduations.  You cannot imagine the
    relief I feel now when I have a half dozen custom waxes cooking and
    don't have to cross my fingers at quenching time. 

    One of the tips I received from an Orchid member was to harden the
    investment by adding Boricx Acid. This helped, but didn't eliminate
    the problem. The draw back was that removing investment from the
    castings took quite a bit of time. I still use the Boric Acid but in
    much lower douses. It seems to give the castings smoother surfaces. I
    use about 3/4 teaspoon per pound of investment. 

    I hope this saves someone the agony that I have gone through over the
    years. 

    Cheers! 
    Robert Hood    

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