overtone versus orient

[Richard W. Wise]

Here is a good one for Zeide to sink her teeth into,

had a call yesterday from a gemologist. he wanted to talk about the distinction between orient and overtone. As I recall the GIA definition, orient is defined as a rainbow effect, that is polychromatic whereas overtone is monochromatic this has me confused.

Fine black pearls will often exhibit a monochromatic overtone, pink, green, blue. Occasionally the overtone is mottled, that is you might see pink on one side, green on the other.

The only time I have seen a true rainbow affect is in very baroque Chinese pearls. Occasionally white southsea will exhibit a bit of pink. I have assumed that this was a result of light interference, that is, light beams bouncing off various hills and valleys in the pearl and knocking into one another. Overtone on the other hand is mainly the result of light diffraction through a grid created by the alignment of aragonite crystals Am I missing something?

 

[Zeide Erskine]

Hi Richard,

Overtone is a secondary color impression and can be enhanced by dying (in that case I call that undertone like the blush effect on akoyas) or vapor deposition. Natural overtone in collector world is called "color spill" and refers to the effect of a pearl having a colored fringe around its shadow when put on a white surface in direct light.

Orient is a prismatic effect and, in contrast to overtone, moves. Although the so-called wild-water orient looks like it is only on the surface as in niobium treated pearls, the real thing in natural and solid-nacre cultured pearls or such with very-thick-nacre can be observed by candling. Just hold the pearls up to an intense white light source and you will observe the rainbow colors inside the pearl through transmitted light. This test also works with dark pearls. Dark pearls with natural orient have to have highly transparent, albeit dark, nacre to create this effect. If you cannot verify the transparency by candling with a 100W clear light bulb, any orient-like effect the pearl exhibits is questionable in its origin.

Zeide

 

[Richard W. Wise]

Ziede,

Placed several freshadama pearls over the contracted iris of my new GIA microscope with concentrated darkfield. Candling taken to the limit.

Transparency: The freshadamas and the Southsea whites and goldens I compared them to all showed a shadow toward the center, kinda surprised me. Only difference in this visual appearance between the CFW, SS and akoya was the fact that you can't see any banding (bead texture). CFW showed some lint like inclusions that seemed to concentrate toward the center shadow. The blacks were opaque, could not see any tranlucency at all.

Color: The slight pink of the CFW and of the SS was enhanced, ie it appeared pinker but no chromatic affect was present.These are exceptionally fine CFW!!!!!

Question: Isn't orient visible to the eye without the aid of candling? If it defines quality it would have to have a visible affect.

 

[Zeide Erskine]

Hi richard,

Orient is visible to the naked eye depending on how the nacre is crystalized throughout the pearl either on the surface of the pearl (soap bubble effect), inside the pearl (warp-on-the-back-of-a-mirror effect), or outside the pearl (colorful halo effect). The problem with candling cultured freshwater pearls (and to some extent South Seas, too) is that they are grown in an environment that is really not all that optimal for their most natural development and thus can cause severe stress making the mussels develop intermittent conchiolin layers in the pearls that can look like bead inserts on some x-rays. Naturals do that, too, in stress situations (typically under salinity and/or heat stress) but you can have some naturals that are entirely transparent while that is near impossible with cultured pearls.

The lint-like inclusions are probably capillaries (pore-like structures) filled with oil. You get that with South Seas, too, but not with akoyas since they do not have enough nacre to even dream about developing such natural features. My freshadamas have distinct pinkish color spill and do show orient (a chromatic sheeting like an aurora borealis) in transmitted light. So, even if mine are not enhanced beyond polishing and oiling, yours may have been enhanced either ex post facto or still in the shell (by feeding the host mussel carotinoid enriched algae). As I mentioned before, if you want ultra pure pearls, you have to grow your own or get some naturals.

Zeide

 

[perlas]

Hi Zeide,

If I may dip in this thread, how will I know if pearls have undergone pinking? How do you "pink" a pearl anyway?

I have bought some nice freshwater pearls with great luster and with orient. Depending on lighting conditions, the pearls may appear white or a pale but distinct pink.

Upon candling, the depth shows a transluscent peach color rather than pink.

 

[Zeide Erskine]

Hi Sam,

Your pearls have probably been sunbleached from an original peach color. Since they have orient, they were most likely not bleached chemically or at least not much. What you describe sounds very much like pearls whose outer nacre layers are clear and inner layers peach.

Please also note that solid nacre pearls always look tan in transmitted light. So, if your pearls are a natural pinkish white (indicating that the host shell was an albino) you will see some yellow shift in transmitted light resulting in a peach impression. Since albinos are quite rare it is more likely that the pearls were put out into direct sunlight for bleaching which will result in a very similar effect.

Zeide

 

[Richard W. Wise]

Zeide,

Sounds like Perlas is describing the same thing I saw, namely monochromatic overtone and a pink glow in transmitted light. I notice that hardly anyone has jumped in on this thread. I suspect that is because a lot of experts are confused about this distinction and, perhaps, too embarassed to admit it.

Be interested in Jeremy's opinion. His lovely "freshadamas" are very fine and have a distinct overtone but no affect that I would describe as "prismatic".

Shall we define our terms: prismatic (Webster) means; multicolored and irridescent, agreed? Irridescent really means the same thing, that is the showing of prismatic (rainbow) colors. Monochromatic means
one color, as single color.

 

[Zeide Erskine]

Hi Richard,

Yes, that is what iridescent means. Natural pearls have always been coveted for their iridescence but in modern perliculture that term has been hijacked to mean either mirror or overtone both often of the Monsanto kind. You should get your sample strand of pearls with full rainbow orient in, on, and around every pearl before the week is out. It is really something you must have seen once to recognize ever after. When you have seen the "teaching strand" you will understand. I had several people ask me whether they were opals before.

Zeide

 

[Caitlin]

Hi Zeide and Richard

You should get your sample strand of pearls with full rainbow orient in, on, and around every pearl before the week is out. It is really something you must have seen once to recognize ever after. Of you have seen the "teaching strand"

This topic of overtone and orient and pinking is the hardest for me- probably as I have never seen top quality strands like that, in person. Is that "teaching strand" a loan out? Is is possible to get a turn seeing it? Or maybe some pictures?

 

[Zeide Erskine]

Hi Caitlin,

I do not have the expertise or equipment to take proper pictures but Richard is definitely free to post as many as he can take or have taken. The teaching strand is a baroque klonk that has at the same time everything that can be right and desirable about pearls and every flaw and foul that can occur in pearls. The pearls are also completely raw except for having been washed and drilled. As such, it is not a jewelry store type of jewel but rather an irreplacable teaching tool for aspiring pearl scholars.

Zeide

 

[Richard W. Wise]

All,
Yes, very exciting, can't wait. Hopefully will be able to get a photograph. Trying to get Fred Ward to join us on this thread and hopefully take a shot at photographing this phenomenon.

Thanks Ziede.

 

[Satine De La Courcel]

Hi Zeide, Richard and Caitlyn

Confused who me??? you bet I am confused!!!! I will have to re-read this thread a few more times before I ask my questions. Some thinkgs click then I read again and it goes away.....

Ash

 

[Zeide Erskine]

Hi Richard,

Since you mentioned that you already saw orient in baroque pearls, I added two pairs of earrings one in round (the slightly smaller pearl has weak orient and the slightly larger one has strong orient) and one in half-drop shape with near extreme orient. Jerin and Slraep may chime in with their opinions since they got some of them, too. (Those were gifts.) However, please note that the ones I just sent you are strictly on loan and I will turn into Hag Nag, Headmistress of Hogwash's School of Bitchcraft and Misery, if they are not returned to me within a reasonable timeframe. The post office gave me a delivery guarantee by Thursday 3.30 p.m. on the express mail package which means you will probably have your package by Saturday or so.

Zeide

 

[pearl guide]

JShepherd just left for Nassau with his son. I have forwarded this thread on to him for comments while he is on the road, if he will indulge us during his vacation.

 

[Zeide Erskine]

Is he shopping for conch pearls? We may need another thread for that. I want pictures.

Zeide

 

[perlas]

Hi All,

I compared several freshwater white pearls with different qualities under intense light source.

1) In fine pearls (lustrous and with orient)
The pearls are more translucent upon candling. Same as Richard's observation, the pearl appears monochromatic with pink glow.

Do we see the monochromatic color because the pearls are highly translucent and thus, we can actually see the conchiolin since the pearl had undergone little or no treatment?

2) In commercially available pearls (lustrous, no orient, but with bleach marks upon close inspection)
The pearls appear "grainy" or with "spots" (Under normal light, the pearls are round with no pits). It is less monochromatic and I saw a green glow rather than pink.

Is this because the pearls had undergone so much bleaching that the conchiolin is lighter therefore appear to be not visible?

3) Low-grade pearls (not lustrous at all)
Appears milky upon candling, can't see anything but milky white.

I also observed pearls with qualities in between and I think that the finer the pearl, the more translucent it is like a jelly opal instead of the iridescent harlequin opal.

Tell me if my observations are supposed to be what they should be or did I miss something out?

The beauty of not being an expert is I can throw in a lot of questions without being embarassed and Zeide is able to tolerate my most silly questions.

 

[Zeide Erskine]

Hi Sam,

You are doing just great. Yes that is exactly it. Unbleached high-grade pearls retain their conchiolin and thus appear a tan-tinted translucent color that concentrates towards the core of the pearl while bleached pearls have their conchiolin denaturized and appear to have residual blotches while overbleached pearls have hardly any residual conchiolin to connect the aragonite crystals and the result is a dull murk.

There is one proviso, though and I hope that Richard and Fred will be able to take proper pictures of that. Pearls of perfect water and orient (that means translucent pearls that have not been bleached) do look more like harlequin opals than jelly opals in transmitted light. Actually they look like a slightly yellow mist with an aurora borealis sheet waving inside them. It took me quite awhile to assemble the "teaching strand" I just sent to Richard so it would include every type of translucency and combination thereof, every type of orient and combination thereof, every type of reflectivity and combination thereof, as well as every type of flaw and foul known to pearl world. I even like wearing it, too.

Zeide

 

[perlas]

Zeide,

I get your drift as I have seen the prismatic phenomenon in other light, naturally colored pearls.

I have YET to see a white pearl that displays the qualities of a harlequin opal. It must be more dramatic. Can't wait for the photographs of the teaching pearls.

 

[Richard W. Wise]

Zeide,
Will of course return the pearls. Fred Ward has agreed to photograph so, with your permission, I will send them to him after taking a goood long look.

Richard

 

[Cam Hatch]

This 'teaching strand' sounds absolutely fantastic. A great tool to have for educating your own staff in the business, but also clients that are new to the pearl market.

I wonder how far you could take it....would it be possible to have a strand that features imitation, freshwater, akoya, japanese and chinese, keshi and south sea?? All the same size and colour?

Can't wait to see the images!