Lapidaryforum.net
Let's Rock => Opal => Topic started by: vitzitziltecpatl on December 12, 2015, 07:06:57 AM
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Thought this might be a good starter link for a new thread. Lots of good info here.
http://www.opalsinformation.com/index.php/opalgrading/opal-identification
Hope others will post informational links here too.
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Just an FYI here. My anti-virus blocked that link due to potential malware.
Doesn't mean the site is bad, but something is causing issues.
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No one else posts good or bad. Norton and Microsucks Smartscreen both say it's okay. Your AV paranoid???
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My antivirus blocks that page also. I use NOD32 by ESET. I have used it for well over a decade and trust it exclusively for my antivirus needs. Something at their site is sending up red flags. Could be related to some of the advertising they have attached to their site.
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Yeah. Link to sign up for their newsletter is at "list-manage dot com". That page is dated from 2009, too. Main reason I put it up was for the drawing of how light is broken up by the structure of precious opal.
Here's another link. This one is from gov. agency in New South Wales, AU - so if this link is bad it's a conspiracy.
http://www.resourcesandenergy.nsw.gov.au/miners-and-explorers/applications-and-approvals/opal-mining/about-opal
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Good info in both links...I get no problems with them.
Here's how to tell a fake opal
https://www.youtube.com/watch?v=2uSZRoAfMgM
https://www.youtube.com/watch?v=2J4Qly4VM3I
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"For red light to appear the spheres must be relatively large (0.0003 mm in diameter). As most opal consists of spheres less than 0.00025 mm in diameter, red is not a common colour. If however, red does appear then the shorter wavelength colours will appear at other angles of viewing. Medium-sized spheres result in green and blue colours; while smaller spheres give violet colours."
Curious to me that smaller spheres give violet colors, yet blue is the most common, while violet is, in my experience, fairly uncommon. Perhaps what they consider violet is something I consider blue?
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Yeah, color perception from one individual to the next is another one of those subjective areas that often lead to lengthy "discussions". Pretty sure that any text technical enough to include the nanometer size of the spheres would likely describe the colors according to their precise wavelengths.
There's another article somewhere out there that talks about the most common colors for various types of opal. Good example of that is how red is much more common in white opal than in black. If I can find that article I'll post a link up here for it.
Good to see you getting the opal itch again. Or perhaps I should be sending condolences for your "relapse"... .
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Well, it may be that the deep deep blue that is common in opal is what they consider violet. I've always considered it blue. lol.
Looking at the wiki page for Violet, when it gets to discussing the wavelengths, there is a "blue" that is officially in the "violet" range that I think qualifies for some of the color seen in opal, but it's not a huge deal. I wonder if purplish violet tones don't show up as much because the size gets *too* small, and the structures have a harder time lining up? I'd be curious to see what the people who study opal on that level think about that. You really don't see purple that often, as I recall.
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Well, it may be that the deep deep blue that is common in opal is what they consider violet. I've always considered it blue. lol.
Looking at the wiki page for Violet, when it gets to discussing the wavelengths, there is a "blue" that is officially in the "violet" range that I think qualifies for some of the color seen in opal, but it's not a huge deal. I wonder if purplish violet tones don't show up as much because the size gets *too* small, and the structures have a harder time lining up? I'd be curious to see what the people who study opal on that level think about that. You really don't see purple that often, as I recall.
Purple and violet in opal are quite rare in my experience. I can't explain it from a technical standpoint but I have what may be a little insight into how the colors are named. First, violet is a spectral color if the old mnemonic I was taught is still right: V-violet, I-indigo, B-blue, G-green, Y-yellow, O-orange and R-red -- VIBGYOR.
But color systems used to describe gem colors vary a lot in terms of names. My old stand-by is the Gemdialogue system but there are several others, Munsell, the now obsolete GIA gemset by Pantone and the new one they've adopted, Gem-e-Wizard along with others. Violet in the Gemdialogue system would be called "B2P/moderate bluish PURPLE."
The best showing of violet in opal I've personally cut is in this crystal opal from Mintabie, Oz. It's hard to capture the exact hue in an image but depending on viewing angle the entire top third of the stone shows a stunning pure violet.
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Now you've gone and done it, Gemfeller! Vince's favorite is Mintabie and now he is going to covet that stone of yours. It's gorgeous! :Worthy:
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Thanks for your compliment Robin. I have problems when it comes to choosing a favorite type of opal or a favorite field -- they all produce stones that make my heart beat faster, even old Coober Pedy white base. But if you ever meet my wife, please don't tell her how close I came to taking a second mortgage on the house to buy an incredible parcel of Mintabie! It was mined when they decided to dig away the original aircraft landing strip and discovered it had been hiding an opal wonderland.
Fortunately I suppressed my impulse which turned out to be a good thing in several ways. First, I didn't have a buyer for such a high-dollar investment; second, I don't think I could ever have sold it once all that beauty was mine (and the bank's). And best of all I'm still happily married with a roof over our heads!
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Hey there, Gemfeller. Thanks for posting about the colors. We had touched on the relative rarity of certain colors in a thread somewhere, and the true violet is rare.
Knew that one was Mintabie before reading the post. Also have some old "Airport" Mintabie. Not the top grade like you referred to, but still cool to have it.
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Gemfella: Might be rare with all the violet, but I like the one in your avatar much, much better.