[Zeide Erskine]

Hi Sam,

Akoyas are near universally treated except for the fancy natural colors and some Korean ones (that come from the closely related pinctada shimitzuensis) that occur in albino rosé. Some of these Korean farms are experimenting with extra long cultivation times and the quality (and price) reflects this. Orient will be destroyed by bleach but polishing does not affect it very much. Oiling seems to diminish orient a little bit and vapor deposition seems to have no effect.

Zeide

[CortezPearls]

This is a very interesting subject, but photos of pearls may lend some help. For instance, you can fully appreciate the Overtone on the pearls in the following photo.
Notice the "halo" effect...it cannot be fully appreciated on this small low-quality photo. Pearls that display at least 3 distinctive (sharp) "rings" or "haloes" are know to have the "Ojo de Pescado" or "Fish's Eye" effect, which made the Sea of Cortez a Legendary Pearl.

Douglas McLaurin
Perlas del Mar de Cortez

[CortezPearls]

Then...we also have ORIENT which is also very hard to capture on a photo since it is a dynamic visual effect that is best seen as you gently move the pearl. In this case, a photograph is a "static" representation that will never be able to give you the full effect.
Nevertheless, some pearls are so full with Orient that some of this incredible beauty -just a mere fraction- will be seen on the photo.

These baroque pearls are over 10mm in diameter and display good orient and overtones. It is easier to "catch" Orient on baroque pearls...their uneven surface allowing for a better play of colors.

Douglas McLaurin
Perlas del Mar de Cortez

[Slraep]

I was under the impression that orient is the result of reflected light and that body overtone is the result of absorbed light.

Slraep

[Zeide Erskine]

Hi Slraep,

Overtone is the result of absorbed light, mirror is the result of reflected light, and orient is the result of refracted light. In your standard cultured pearls, you typically have only one or at best two of these properties but orient is hardly ever one of them. I am glad you appreciate your object lesson in water, mirror, and orient. You really must have seen pearls that are absolutely untreated while simultaneously being of high quality to fully appreciate what the old masters were so keen about. My standard for pearl earrings is that if Vermeer saw them he would have wanted to paint them.

Zeide

[Cam Hatch]

Hi Richard & Zeide

Any luck with the photography of the strand??

[Slraep]

Originally Posted by Zeide Erskine

Overtone is the result of absorbed light, mirror is the result of reflected light, and orient is the result of refracted light.

So, the quality of mirror would consist of uniquely reflected light. The orient, on the other hand, would be due to light comming into the pearl, getting distorted by the floating layers/sheets of aragonite crystals and comming out refracted as if through a prism(thus the rainbow effect). The thinner the sheets of suspended aragonite crystals, the better the orient. The more of these thin suspended aragonite sheets, the better the orient.

Sometimes one can see the multiple thin concentric sheets of aragonite very easily. Between these aragonite sheets there is another colourless, translucent sheet of various thickness. What is this translucent sheet? Is it conchiolin? Or is it just a trick of light? There should be very little conchiolin compared to aragonite.

Slraep

[Zeide Erskine]

Hi Danuta,

The layers inbetween or what looks like layers inbetween are more aragonite layers where the individual aragonite crystals are facing in another direction. Hence the refraction. It makes me happy when other people finally understand why I want my pearls unprocessed.

Zeide

[Slraep]

Originally Posted by Richard W. Wise

Ziede,
More on this conchilin thing. The bleaching eats the conchilon? My understanding is that conchilin is a glue like protein binder although some call it calcium carbonate, that is between the aragonite layers.

Hi Richard,

Conchiolin is an organic protein. It is not a mineral, and so it cannot be any kind of calcium carbonate, even if some call it that. It is the aragonite crystals that are a type of calcium carbonate, in orthorhombic(twinned) crystal form.

Slraep

[Slraep]

Originally Posted by Zeide Erskine

Hi Slraep,

The layers inbetween or what looks like layers inbetween are more aragonite layers where the individual aragonite crystals are facing in another direction. Hence the refraction. It makes me happy when other people finally understand why I want my pearls unprocessed.

Zeide

Okay now, the transparent layers have been demystified! It couldn't be conchiolin because the percentage of it in a fine pearl compared to aragonite is just too small.

Slraep

[TeNatura]

Hello All,

What a wonderful thread, I love it when the forum talks specifics and shares the fruit of their experiments!

In researching this further I came across an article from the International Electronic Journal of Optics that goes into great detail about iridescence and diffraction in pinctada margaritifera shell and touches upon how this pertains to orient.

Well worth the read for the photos!

http://www.opticsexpress.org/DirectP...TOKEN=61265618

A conservation biologist friend has offered the use of his microscope (with attached camera), if we get around to some photos next week I will post pictures.

Cheers,
Kristen L. Andersen
-----------------------------------------
Creative Director/Founder
Te Natura
http://www.tenatura.com

Read Kristen's Blog: "Exquisite - Conscious Style and Living"
http://www.kristenandersen.com/weblog

[Richard W. Wise]

I read the article a few years ago. Excellent explanation of the phenomenon.

Wit Ziede's indulgence, Jeff Scovil will be here photographing for two days beginning August 15th. We will take a shot at photgraphing orient then. If that doesn't work, will send the pearls off to Fred Ward.

Kudos to Douglas for a couple of excellent images. The Baja pearls have improved greatly since I first saw examples at the Hong Kong Show five years ago. I love that reference: "Ojo de Pescado" I take it that has some history behind it. Great stuff for when I get around to revising Secrets Of The Gem Trade

[Slraep]

Interesting articles, Kristen. They are using nacre which is flat/
horizontal, as in MOP or shell, to measure diffraction and interference. It must be a little different when measuring diffraction and interference on a spherical or curved pearl where the nacre forms
curved sheets. Something must happen on the edges of those curved sheets, too, where aragonite crystals are perhaps not so densely packed or flattened . Think of an onion or cabbage vs layer cake.

Slraep

[effisk]

(I edited my previous post, just thought 200 pearls wasn't that many after a better look at the necklace)

[Richard W. Wise]

Ok, no luck with Scovil. Will now send the teaching set to Fred.