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Post by parfive on Aug 14, 2012 21:12:23 GMT -5
Not too impressed with the old pic . . . . . . so I tried for something better. It’s night out, can’t experiment with sunlight, so down to the basement. The iris goes all the way around this puppy but I still can’t get a good pic of it. First shot is holding a Mini Maglite behind the slab, and these two with a small photo light behind.
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jspencer
freely admits to licking rocks
Member since March 2011
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Post by jspencer on Aug 14, 2012 22:45:48 GMT -5
The information I have read state that a non-polarized light is the best for viewing the iris effect of agates. They are also easier on the eyes.
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Post by parfive on Aug 15, 2012 3:25:15 GMT -5
Yeah, non-polarized would cover all these descriptions. Michael Carlson: Although the best light source is a bare filament incandescent bulb, the effect can also be seen when using sunlight.Exactly what Rocpup called for in his iris post I also see it described as a distant point-like light source or a transmitted incandescent source. Scroll down about 1/3 of the page for the iris section. (Polarized light specified for studying agate sections under a microscope.) www.quartzpage.de/agate.htmlSome more technical mumbo jumbo. www.minsocam.org/MSA/collectors_corner/arc/iris.htmPete Rodewald gave a good presentation on iris agate at the Wisconsin agate show in 2008. I was gonna watch it again just now but unfortunately, it looks like his presentation didn’t make it on to the DVD set filmed at the show. His iris pictures are featured in Carlson’s and Johann Zenz’s agate books.
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unclem
starting to spend too much on rocks
Me
Member since August 2012
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Post by unclem on Aug 15, 2012 7:53:39 GMT -5
Great pics!! I have tried a few of these, Mini mags, sunlight. But not making it. I guess I cant take iris agate off my bucket list yet. :/
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unclestu
Cave Dweller
WINNER OF THE FIRST RTH KILLER CAB CONTEST UNCLESTU'S AGUA NUEVA AGATE
Member since April 2011
Posts: 2,298
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Post by unclestu on Aug 15, 2012 8:19:11 GMT -5
Now that is one heck of an Iris Agate. I wonder if the effect would be picked up if place on a light box. Probably not Stu
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rocpup
spending too much on rocks
Pink Limb Iris
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Post by rocpup on Aug 16, 2012 13:30:39 GMT -5
Nice re-post. The reasons behind the rainbow can be overwhelming to most of. I just enjoy it. Don
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Post by helens on Aug 17, 2012 21:03:17 GMT -5
Neat! So if you find an agate with a LOT of banding in a blue/white color, odds are better of finding an iris. Do iris's ever occur without the banding? Non-polarized light... isn't all light non-polarized? As in plain light bulb??
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Deleted
Deleted Member
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Post by Deleted on Aug 17, 2012 23:15:16 GMT -5
Gorgeous pics!
Helen: a lot of tight banding does increase the odds, but doesn't guarantee that you'll get an iris. The effect can occur in any color highly translucent agate. The effect does not occur without the banding, although the banding can be so fine that it is invisible without magnification.
Some light, such as LED's or lights that are behind filters or polarized glass, are quite directional (not a lot of scattering). At least in my experience, a directional light source will sometimes produce an iris effect where none could be seen with more diffuse backlighting. Generally, though, I agree that strong diffuse backlighting produces better iris colors. Sunlight does a great job if you can mask off the edges, though the blinding brightness is a strain on the eyes.
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Post by helens on Aug 17, 2012 23:20:33 GMT -5
I have several clear agates with strong banding that's barely visible normally because they are white... but some have these interesting sort of bubble patterns more than lines when held up to the light, and it looks yellowish, not rainbow. Was wondering if some of those might be iris's and I'm just looking at them with the wrong light:)?
I have several brazillians with a similar pattern to the one that rockpup posted for a limbcast... I have to check them in sunlight!!! I'd love to have an iris one, but I'm not going to hold my breath:). I already have a shadow laker, and I wonder if it's also an iris actually, because different colors DO come through the bands, it's just not sliced flat, it's like a cheese wedge.
Thanks rocks2dust:).
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peachfront
fully equipped rock polisher
Stones have begun to speak, because an ear is there to hear them.
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Post by peachfront on Aug 18, 2012 17:44:49 GMT -5
Awesome...!
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Minnesota Daniel
freely admits to licking rocks
A COUPLE LAKERS
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Post by Minnesota Daniel on Aug 18, 2012 20:22:28 GMT -5
Helen, I just looked it up, when the iris effect occurs, the nearly invisible banding will be in the range of 400 to 10,000 bands per inch. You can't see it with the naked eye, or even a hand lens. Shadow agate banding is one or two orders of magnitude less dense than that -- it's a completely different phenomena.
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Post by helens on Aug 18, 2012 20:28:05 GMT -5
Helen, I just looked it up and for the iris effect to occur, the nearly invisible banding will be in the range of 400 to 10,000 bands per inch. You can't see it with the naked eye, or even a hand lens. Shadow agate banding is one or two orders of magnitude less dense than that. OHHHH!!! So basically, if you stick it under a microscope, you have to SEE banding not visible to the naked eye for it to have the rainbow effect? I have a microscope... with a single point backlight! Will check that! Thanks for the info!!! Wait, even if I see that dense a banding... shouldn't it show rainbow in the light anyway? Nm, I'll dig up all my thinner clear slabs and look under the microscope first! Thanks much for the info:)!
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Post by drocknut on Aug 18, 2012 22:29:44 GMT -5
That is really cool, I've never seen one with the iris all the way around the center before. Glad I saw this post and thanks for showing it off.
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Post by Rockoonz on Aug 19, 2012 0:05:15 GMT -5
The bubble effect, we call it turtleback, doesn't iris to my knowledge. The rainbow effect shows the best on super thin slabs and is from the slab acting as a prism. magnification doesn't help, and iris is rare, maybe like 1 in 1000 of the right type agate will iris, and then only if cut in the perfect direction.
Lee
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rocpup
spending too much on rocks
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Post by rocpup on Aug 19, 2012 12:29:03 GMT -5
One in a thousand to one in two thousand makes "Iris Agate" indeed rare. I know little the effects of polarized or non-polarized light has on a slice of agate. Again the rainbow effect is BEST viewed with the use of a CLEAR incandescent bulb of 25-40 watts in a dim lit room not black. The slice of a thin cut translucent agate is held up to the light tilting it back and forth to get it to the best viewing angle. The slice must be polished or a liberal coating of Three-in-One or Olive Oil. The coating must have the same refractive index as agate for it to work properly. WATER or many saw oils will not permit the light entering the agate to be refracted into the show of color. If after the above and there is no rainbow no amount of polarized filters or microscopes is going to make any difference. Cutting a slice less than 1/16 inch can be difficult and my experience cutting it thinner has little effect on the outcome of color. I do have some great slabs of Brazil agate that are 3/16-1/4 inch thick and exhibits a great rainbow. I have tried to split Brazil slabs to get a better look with mixed results and will not try again. I have cut some of my iris rock 3/16 to cut cabs from it. Iris needing back-lit does not lend itself well to jewelry. I do have a large collection but I have been looking for fifty years. If you do not see color the turtleback is also beautiful so all is not lost. Grab another agate and try again. No one needs to tell me how rare it is. I have about 300 pieces so you know I have kissed a ton of FROGS. Don
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Post by helens on Aug 20, 2012 12:33:33 GMT -5
This is such great info here! I have such a mess of rocks EVERYWHERE right now (in the midst of sorting) that I have to put everything away before I can pull out and sort the 'possibles'. Odds of course are good that I don't have a single one, LOL! Doesn't mean I shouldn't check:P.
Getting the (I hope! Display cases are expensive!) last of the display cases soon, then I can sort my rocks and pull out all the possibles to check at once:).
Glad to hear about the water being useless!!! Gives me a little more hope for the very banded ones I've already checked:).
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