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Colour change cobalt spinel?

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A client of mine has this piece of rough cobalt spinel, 33cts. (He is calling it cobalt, not me)

Have any of you cut material like this?

I have seen plenty of emerald rough that looks like this, a ‘mish mash of crystals’ and I know that in Colombia cutters won’t touch the stuff unless it’s filled with gemetrat first. For obvious reasons this is not ideal.

So… cut a cab or leave it rough or ???

Three ideas, the first of which gets deep into color theory. (The life of graphic design.)

  1. If you have the means to identify whether any of the interior crystals are larger than the rest, you might be able to separate the individual crystals. After which you could cut them individually. This specimen, if you can find crystals you can work with, would make a nice batch of color change accents for a larger stone. The blue/purple would provide nice subtle accents to red, blue, or violet stones. White light color looks to be blue-violet, allowing for matching to some green stones, and would probably require a yellow gold setting, and/or additional yellow accent stones. Green matching in this manner would make the setting feel very “Mardi Gras.” While matching to ornage would provide a very sharp contrast, getting the exact right orange that works well under all lighting conditions would be very unforgiving.
  2. Semi-cab for ring or pendant: flatten the side that is already the closest to being flat, then gently round all other rough edges in order to preserve the over-all shape of the stone. Maybe consider using UV-resistant binders to help stabilize the stone.
  3. Semi-cab for earrings: gently round until two sides of the stone are symmetrical, then cut along the line of symmetry.
    Additional thought: If binders are used, maybe use red or green tinted binders prior to cutting. This will add a nice color-stable veining contrast to the work. (sorry more color theory).

Thanks so much, have you cut much material like this?

I’m concerned that without Gemetrat or something similar it will just keep flaking apart.

Are you positive this is Spinel? Whats the S.G., R.I. and Spectrometer say exactly?

  • Mike Acquire Collectibles