overtone versus orient

[TeNatura]

A little light reading...

A little light reading...

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/Direct...id=63375&seq=0&CFID=29036457&CFTOKEN=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.

 

[perlas]

Ziede, et al,

Examined the pearls under magnification. They have an appearance that differs from the freshadama strands, they have no central shadow and they dont appear pink in transmitted light. If anything the pick up a bit of veining like the green veining in our skin. However, the round ones do have a central shadow and also turn somewhat pinkish so this may be a function of the shape.

Richard,
When are the pictures coming? Everyone is interested on this thread. Thank you for sharing your observations.

Zeide,
I have seen a white, roundish, untreated pearl with high orient as you have described..like harlequin opal. However, no central shadow is present or was I mistaken? If not, then high translucency is possible in white, round pearls without having a central shadow. The pearl I saw has a greenish glow rather than pink. Most pinks I see are sunbleached.

It seems that a central shadow is more defined in sunbleached pearls than in untreated pearls.

 

[Zeide Erskine]

Hi Sam,

Yes, you do see the central cavity shadow better in sunbleached pearls because the UV irradiation breaks up the conchiolin into smaller bits that render the pearl more transparent. Typically the lack of central shadow is indicative of natural pearls, but you can also have cultured pearls without central shadow if they are entirely grown from donor tissue. The greenish cast most likely comes from using a bluish light source or less likely from accumulated chlorophyll which can happen when the culture pond was overfertilized.

Zeide

 

[Richard W. Wise]

All,
I must apoligize I completely zoned out on this. In the iddle of a major renovation of my house. Fred Ward's photos were disapointing. I posted one on a blog post: http://gemwiseblogspotcom.blogspot.com/2006/09/choosing-perfect-pearl.html. Fred was unable to capture the rainbow orient on Ziede's pearls. I used a couple of images we took of Black southsea and Chinese freshwater. The Tahitian shell show distinct orient.

 

[BlackPearlDudeDC]

After reading through this...I was very curious to see the pics.

 

[Pareltje]

Yes, please post pictures. Preferably high quality pics.

 

[Katbran]

It's a pretty old thread - interesting discussion. I came after Zeide was gone... I seem to remember there was a problem.

 

[Fiona]

I recall she wasn't real and also had other characters she played on here that had conversations with one another....

 

[BlackPearlDudeDC]

Well that isn't creepy at all...sheesh. Still after all that reading I wanted to see pics. I posted my annoyance lol.

I recall she wasn't real and also had other characters she played on here that had conversations with one another....