BI-color natural pearl ?

[Isi]

Hello everybody. This item has been sold in an auction house recently.
http://www.pestel-debord.com/html/fiche.jsp?id=6921927&np=1&lng=fr&npp=10000&ordre=&aff=&r=&sold=
Look at the material making the jug. It is announced as carved in shell, but I went to see it and to me it strongly looks like an entire pear-shaped pearl, only a bi-color one (not 2 pieces glued together).
Have you ever seen such a thing ?
Do you think there is any chance that it could be natural ?
Thank you for your opinions !

 

[MSC]

To my eye it presents as natural...

 

[Lagoon Island Pearls]

Bracelet en argent (925 millièmes) composé de petites perles de culture grises irrégulières et retenant un motif en pendeloque figurant une aiguière la panse composée d’un coquillage sculpté et la monture en argent (925 millièmes) sertie de diamants taillés en rose. XIXème siècle.

My French-Canadian translates this as : 925 Silver bracelet composed of small gray irregular cultured pearls and pendant motif representing a ewer, the body composed of a carved shell and a 925 silver frame set with cut pink diamonds. Nineteenth century.

I don't see pink diamonds, but perhaps it's meant as a through type diamond setting at the level of the pink/bronze nacre. Isi, can you clarify this translation?

Nevertheless, there's a lot of ambiguity in this description. First, cultural operations were not commonplace in the 19th century. Second, the nacreous and proteinaceous/prismatic surfaces of the pitcher suggest Pterioda or Pinna origin. (Black lipped oyster or pen shell). The symmetry of the piece supports cultural origin which would likely be mid 20th century. Now, if by some fluke this was natural origin, I'd observe some distinct features, namely a pronounced transitional growth front along the margin between the different surfaces. It's not the best image, but the margin of nacre presents as gradual and inclusive as opposed to terminal and superior. In other words, features I'd expect to observe in cut shell. As such, I have my doubts it's a loose natural pearl, but concede it may be a natural blister. However slightly. It's more likely a cultural aberration.

Now interestingly enough, the description of the tiny pearls is also suspect. The dimensions are not provided, however they are not typical of cultural origin, no less the period. They present as non-nucleated freshwater pearls from a much later era with flat spots, potato shapes and ripples, but bearing some resemblance to natural river pearls, especially if the suggested period is true.

In either case, both types are drilled, hence destroyed from a scientific standpoint. This disqualifies most analysis protocols, leaving mainly subjective entries. Additionally, France has very strict requirements stipulating natural pearl origin. In the absence of scientific data and tangible provenance, it's possible they've worked around indeterminable properties to make the item saleable.

The description does not purport natural origin. As such dispels nefarious or inadvertent intent.

Thank you for sharing it with the group.

 

[Isi]

I agree that there is some inconsistency in the description. The first of it being : Cultured pearls for an item dating from the XiXth century. This was the first question I asked to the selling team. The reply was : as long as they have no proof that pearls are natural, they describe them as cultured by default (because the french legislation is very strict about natural pearls and they don't want a sale to be cancelled because of that).

Rose cut diamonds refer to an old style of cutting diamonds, not to the pink color. I know there can be a confusion in the translation word to word

The clasp of the bracelet looks very modern too IMO.

To me when I examined it, the ewe (which was my main subject of interest, not the tiny pearls) looked like a pearl, not carved nacreous material. I agree too that the perfect symmetry suggests more something like a cultured pearl. But is it possible that a cultured pearl would be so perfectly bi-color ? Are there reported examples of this phenomenon ?

All in all, with all its inconsitencies, mixing of data and dates, I find this item very intriguing. At least, nobody from the auction staff, and nothing in the description, suggested that there was anything natural in it.

 

[Lagoon Island Pearls]

Rose cut diamonds refer to an old style of cutting diamonds, not to the pink color. I know there can be a confusion in the translation word to word

To me when I examined it, the ewe (which was my main subject of interest, not the tiny pearls) looked like a pearl, not carved nacreous material. I agree too that the perfect symmetry suggests more something like a cultured pearl. But is it possible that a cultured pearl would be so perfectly bi-color ? Are there reported examples of this phenomenon ?

Thank you for the clarification. That makes much more sense, but still at a loss how it applies to a silver piece inserted into a carved and drilled shell, but I digress.

I've attached a crude diagram of a natural growth front and a cut shell. Figure 1 shows a superior termination of the nacreous layer. If I were to cut a section of Figure 1 and rotate it 90 degrees, you can see a representation of this in Figure 2. The diagram clearly shows a bisected line along the margin where two structures meet. Conspicuously absent are growth fronts. Shells and pearls grow in concentric layers, not linear abutments.

This why pearls can never be faked from cut shell, even with precision cutting and polishing.

So yes, a pearl can be two colors from an incomplete transition in structural layers at the time of harvest, but growth fronts will always be present. In fact, all shells present in this manner. From a microscopic viewpoint, prismatic layers are long laths of calcite, whereas nacre is comprised of shorter, hexagonal tiles of aragonite. Two very different structures. Their length and width can be measured against the radial axis of the shell itself. Prismatic lathes are always perpendicular to this axis. After all, they lay flat on the newly formed layers, like the boards of a floor or deck. We would never construct a floor by standing boards on their ends. A mollusk would never do that either. Visible "end grain" clearly denotes cut shell.

 

[Isi]

Thank you very much for these explanations Dave.
There is on Karipearls website a small bi-color natural pearl for sale :
http://www.karipearls.com/natural-pearl-for-sale.html
Is the groove in the middle, separating the 2 parts, what you call the "growth fronts" ?

In the case of the ewe, there was indeed a tiny groove separating the 2 colors. At first I thought this could be a mark of glueing, but after examining more closely with a loupe, no, there seemed to be continuity in the material.
I regret not having had more time and better, more quiet conditions to examine this item, in a better lighting and with better magnification.
Maybe I should have put a bid on it too. But it seemed expensive for something very uncertain !

 

[Lagoon Island Pearls]

There is on Karipearls website a small bi-color natural pearl for sale :
http://www.karipearls.com/natural-pearl-for-sale.html
Is the groove in the middle, separating the 2 parts, what you call the "growth fronts" ?

No. Those grooves are from a prolapse of the pearl sac. A growth front is more like an edge or drip of paint over another color (surface).
Notice the edge of the nacreous surface next to the black prismatic surface. The other lines toward the left are older growth fronts, painted over by the newest layer.

 

[JerseyPearl]

Dave, as always, your illustrations are illuminating! I am like a moth to a flame when I read your posts.

 

[pattye]

Fascinating discussion, thank you for the great photos and diagrams, Isi and Dave.

 

[Isi]

Yes, thank you very much Dave. This is very clear.
That does not solve the mystery as to what this thing could have been. But that tells us what it could not have been !

 

[pearlescence]

The jug is a later addition. It's not integral but just attached with a jump ring (at least as far as I can see)

 

[SunSeeker]

How interesting! Dave, Isi, thanks for the diagram and detailed explanations.