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I have some small pieces of Australian lightning ridge opal I'd like to make into cabochons.

Normally, I'd use jeweler's wax from my electronic dop pot, but I've heard that opal is very heat sensitive, and can very quickly lose play of color if it overheats.

If I use black dop wax, which I think has a lower melting point, is it safe to use on the opal?

Is there a safer way?

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Green dop wax is best. Don't use glue. I read something about colour loss up there, god knows what they are on about this is untrue. Opal is relatively soft, treat it with care.

To get the stone off again, leave it in the freezer for half an hour to harden the wax, it will pop off.

I grew up on the field in Lightning Ridge and found, cut and sold my first opal when I was seven years old. I have 35 years industry experience. I say this to give you a base line to judge the value of my advice against others who might say otherwise.

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  • I suspect that when I wrote this I was getting confused on the danger of opal cracking when overheated, rather than losing play of color (although I could swear I've heard that claimed as well). I've since learned that overheating is a problem usually associated with opal from non-Australian sources (US opal, Welo opal, etc.). Lightning Ridge seems to have well earnedit's reputation as the world's best :). Thanks for the advice...cheers!
    – Beofett
    Sep 30 '17 at 23:49
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Opals from the Lightning Ridge area of Australian are known for being very high-water-content. Unfortunately, this makes them the most susceptible to heat cracking and related damage.

The danger is not just in color loss — you can crack or crumble stones from this region much more easily than opal from other regions.

You can read the same in Eckert's "World of Opals".

You need to make a business decision regarding how much of your inventory you can practice on, in order to learn how to work opal from this region. How much can you lose before the cost is identical to selling your inventory to someone who has practice cutting, and buy pre-cut from them?

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  • This is good info, thanks. The fragile nature of the material is why dopping is important. While I do much of my work "free form", dopping the opal will give me finer control and let me use a lighter touch. Do you have a suggestion for dopping the material to avoid or minimize heat cracking and color loss?
    – Beofett
    Apr 26 '16 at 23:20
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Based upon discussion with some other opal cutters, what I've wound up doing is to use simple white glue to dop the opal (frequently to the head of a nail, instead of a wooden dowel, but for larger opals a dowel works well enough).

I then apply a thin seal of instant glue ("crazy glue") as a seal around the base of the opal, to protect the white glue from the water while I'm cutting.

Once I'm done, I dip the opal into turpentine briefly, to dissolve the instant glue seal. Then soaking it in water for a minute or two dissolves the white glue, releasing the finished cab from the dop.

The brief immersion in turpentine seems to do no harm to the opal.

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