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Author Topic: Is Gray Opal common?  (Read 680 times)

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John Robinson

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Is Gray Opal common?
« on: September 20, 2017, 08:33:13 PM »

I have 7 pieces of gray opal, but I can't seem to find out anything about it. I have made cabs with three of them and wonder if the smaller four are worth messing with right now(?)

*IMG_1708.JPG (115.09 kB . 475x600 - viewed 144 times)

I ramped up the vivacity on this photo so the color would show
*IMG_1709.JPG (81.04 kB . 450x600 - viewed 149 times)

Actually I have eight, the eighth one has a  color bar that sits on a layer looks nearly black(?) I have been tempted to grind the color bar done to that layer to see if a better pattern emerges

*IMG_1718.JPG (68.39 kB . 600x582 - viewed 141 times)

*IMG_1719.JPG (62.52 kB . 467x394 - viewed 146 times)


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Re: Is Gray Opal common?
« Reply #1 on: September 21, 2017, 05:53:49 AM »

Grey is a thing. One of Paul Downing's books actually has a diagram going from black to white you place your stone next to and compare. Grey is more valuable than white but less than black.

1. Do not grind through the color bar. Looks like you have some really nice rough(and you are taking better pics of opal than I am currently). If you are talking about the last pic with the stone standing on end, do not grind that down. Your money is in the weight of the stone. That looks like a fairly decent color bar and you want to save as much as possible.

2. Remember you are working opals, not making cabochons. You aren't trying to make a big dome. Its a pain in the butt for me to switch mind sets when I go back and forth from opals to traditional rocks because the process is similar yet very different. I try to remember when I switch back to opals to do a practice opal first to get bact in the mindset. You want just enough dome to polish. That's it. Stones look almost flat with a barely perceptible dome to them. The idea again is to minimize what you grind off to maximize the weight. SEDA opals has a video they took when they were polishing a black opal and you can hear one brother telling the other brother who was simply trying to clear a tiny bit of potch, "You know each time you do that we are losing a hundred dollars right?" "Yeah I know." And then he repeats it several times as the brother does very light swipes over the wheel. You can tell he is getting aggravated although the end stone was amazing.

3. Even small opals are worth messing with. I made a really shiny one last night that was half the size of a pencil eraser. It will look good as part of some combination jewelry I am sure when I get around to making it. If anything its good practice, and even better its really quick and time efficient. I spent maybe 5 minutes getting it from the 260-3k wheels last night.


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Re: Is Gray Opal common?
« Reply #2 on: September 22, 2017, 11:23:50 PM »

The price of semi black or gray opal falls somewhere between white and black and usually underneath good quality crystal that is a bit closer to the price of black.  From some not all opal fields semi black opal is known to be less stable for some reason, so more likley to crack or craze.  The one opal with the black backing is from Mintabie in the center of Australia just south of the Northern Territory/ South Australian border around 200k north of Coober Pedy.  Mintabie opal is among some of the hardest and oldest on earth aside from Brazil.  I would be willing to bet that some of the other opal in your photos are as well.  Mintabie opal is a very tricky stone to cut and early on in my carrier I cut and messed up a lot of it.  Most of the time opal from this field has many different tightly pressed color bars some are better than others and some are jelly opal with just sun flash color in them.  Mintabie opal should usually be cut to the best bar and then thinned out so that the good color is just barely see through and the color from the other bars acts as your backing.  On occasion Mintabie is skin to skin color and can be cut with a dome.  Many times Mintabie black opal is actually better faced from the dark potch side so the exact opposite from Lightning Ridge.  That opal with the black on it will not cut as a black opal so dont risk it,  the color bar is nice but the potch is curved and the color has milk in it so if you take it down you will end up with a stone with a varying body tone dark in the middle and lighter on the outside.  You have to be careful after cutting Mintabie and going back to other opal to not grind to quickly because of the difference in hardness. 

I wish I had a whole barrel of Mintabie opal to hold onto and cut, that if a field that is drying up a bit for different reasons not for lack of opal.  It is a fun type of opal to cut once you get the hang of it and it can be very rewarding.   
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