[Jewelry making - Article 01052] - Re: [Orchid] Brittle Carnelian

[Terry Ogden]

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Harry

    Depending on the size of the stone I will go as much as 5 hours at
    around 550F and then turn off the kiln and let it cool with the door
    closed. I do it to maximize color. The stone will be brittle after
    heating that is true. Most of the stuff I get is such and ugly gray
    until heated, I could not imagine messing with the stuff were it not
    heated. 

    I never grind dry, I don't even begin grinding until the wheel is
    evenly wet and the same with my sanding. I have had no problems with
    cracking though, how I noticed that it was more brittle was in the
    course grinding, it would chip more than a non heated stone. 

    I don't know what you mean 'without regard to the integrity of the
    stone'. Under 350F the color does not come out, or it goes brown,
    550F seems to give the best color change for me, so if you want the
    color, that is the temperature you use, and the stone will be come
    brittle. Higher temperatures, and there is enough moisture in the
    stone they will break apart. If they have pockets they will break
    anyhow, but the crystals do something really unique in the way of
    coloration. As far as the integrity of the stone, to me it is like
    any other stone you work with, what you make from it has to be in
    balance with its characteristics. It would not do well to make a very
    thin disk of turquoise and then not back it, it would break or
    crumble very easy. If you know the stone is brittle, or has a very
    strong cleavage, your make it thicker to allow for it, or you
    mechanically protect it. Simply cutting the stone alters it integrity
    from what it was. I have a green stone I really like to work with,
    but don't cut it in advance, the slices "dry" and will split, if you
    cut it and then immediately work it to shape and finish, it does fine
    and I have had no pieces crack even after several years, it is just
    the characteristic of that stone. 

    Another thing is most stones will contain water, and they will dry
    and crack, it is not only Opal that is prone to this. Usually
    finishing them slows the evaporation or seals the surface that I have
    only seen one stone that cracked after completion. Wait till you get
    a chance to work on really fine grained dense Jade, that one you have
    to make shellac wheels to work with. It was the most expensive 12
    hours I have ever had in my life short of surgery. 

    Don't know if that answered your question, but it is what I have
    observed in the cutting I have done. Also, you might want to start a
    notebook on the stones you work, what you notice and how they react
    to your efforts, it will help in the long run and keeps down the
    learning curve. There is a world of differences in the same stone but
    from different locations on the planet. 

Terry
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