Distinguish between salt and freshwater pearls with mg strips and hydrocloric acids?

[Jan Asplund]

I have heard that it is possible to distinguish Saltwater from Freshwater pearls with a simple test that is said to be nondestructive. It tests the amount of manganese wich is greater in freshwater than in saltwater pearls.
Mangansese teststrips are used together with dilluted hydrocloric acid. The acid is put on the pearl and the manganese strip is swiped over it, if it gets a reaction the pearl is freshwater.
Does this test work?

 

[morphius]

I may be wrong on this, but it was my understanding that both freshwater and saltwater pearls contains trace amounts of manganese...just that freshwater pearls contain higher trace amounts of the element.

I myself am not aware of any home 'acid test' that would be able to distinguish the difference in the amounts of manganese, but I would most certainly not recommend playing around with hydrochloric acid (HCL). You would need to achieve a dilution ratio of around 95% distilled water (or more) to 5% HCL (or less) before the acid content was no longer corrosive to human flesh...and you would need an even higher dilution ratio before the solution was no longer actively corrosive to the surface of a pearl.

For instance, wine is around 0.1% acetic acid...an acid concentration high enough to be corrosive to pearls. HCL however, when comparing exact same acid concentration amounts, is much more corrosive that acetic acid.

Given that, for this test to work, the diluted acid test would still need to be strong enough to dissolve some of the surface of the pearl in order to pull manganese from the pearl in order to be read by the strips, in truth, you would be doing damage to the pearl's surface...and decreasing it's value.

I would instead opt for viewing the drill hole under 30x to 60x magnification to see where the saltwater layer ends and where the freshwater mollusk bead begins...since the layer is not very thick.

 

[morphius]

For those interested, I also just confirmed with my wife (who's in her 3rd year of University, studying as a chemist)...

So...if you were able to achieve an HCL dilution ratio which was still strong enough to dissolve a micro-layer of the pearl without causing any visible damage, the HCL would be strong enough to also break apart the atomic bonds of the manganese...meaning the manganese would be dissolved as well, and the chances of it being detected by a test strip would be hit or miss.

 

[Lagoon Island Pearls]

a simple test that is said to be nondestructive.

Acid testing is considered destructive, afterall it etches the surface.

Conclusive analysis requires adequate control groups and baseline data.

 

[pearlescence]

Most of the time I can tell by looking at them...

 

[Lagoon Island Pearls]

Most of the time I can tell by looking at them...

That's subjective though. The OP is inquiring about objective analysis.

 

[Jan Asplund]

Thanks for your inputs, I agree that it seems odd that an acid test on pearls could be considered nondestructive. I have yet not tested this myself and I do not know of anyone who has, I was told about this test by someone who in part had heard it from someone else and none of us know of any actual test results. Also, I do not know how much diluted the HCL is supposed to be.
As I have understood freshwater pearls contains about three times as much manganese as saltwater. I find it doubtful that the same ratio is true for all kinds of freshwater/saltwater perls, I think the amount of manganese in any water must depend on many different circumstances and both salt and fresh pearls do contain manganese wich still would make a test like this more indicative than conclusive.

Though I think the idea of this kind of testing is interresting, as manganese is an element it should still be detectable even when the atomic bonding is lost. Might be possible to develop this or similar testing further?

The reason I asked this question is that a few months ago I bought some very nice nucleated freshwaterpearls wich I have realised that I would have had no chance to for sure distinguish from Akoyas if I did not know. If I can look down a drillhole it ofcourse makes it less difficult but when identifying pearls set in jewellery like rings and earrings I find this realy hard and a simple test would be a blessing.

 

[Caitlin]

Hi Jan
Welcome. That was a most interesting question. I hope to hear followup and/or other methods for making that kind of determination. It would be great if you didn't have to go to a gem lab but be able test a pearl for content as you do gold and silver.

 

[morphius]

Though I think the idea of this kind of testing is interresting, as manganese is an element it should still be detectable even when the atomic bonding is lost. Might be possible to develop this or similar testing further?

Just to provide a little deeper explanation...according to the mathematics of chemistry, (again assuming the HCL is of a concentration high enough to impact the pearl), the HCL would cause a molecular breakdown of the calcium, the manganese and itself (being hydrogen and chlorine). The resulting reactions to the manganese that is present, would most likely result in a chemical compound of manganese-chloride + hydrogen ion...which would most likely present as a gas and evaporate as it was produced.

 

[Lagoon Island Pearls]

...which would most likely present as a gas and evaporate as it was produced.

Right. In which case only chromatography could measure concentrations of each element.

Also, there would have to be reagents present in the solution of any visual test to indicate the presence of targetted elements above or below certain levels.

I'll stick to polarography, albeit destructive.

Sometimes, for the sake of a cultured pearl strand, it's acceptable to sacrifice one pearl.

 

[morphius]

Right. In which case only chromatography could measure concentrations of each element.

Also, there would have to be reagents present in the solution of any visual test to indicate the presence of targetted elements above or below certain levels.

I'll stick to polarography, albeit destructive.

Sometimes, for the sake of a cultured pearl strand, it's acceptable to sacrifice one pearl.

Ah yes, i had totally forgotten about chromatography...nice catch.

But I agree with the OP starter...it would be fantastic to be able to determine freshwater versus akoya definitively (and without destroying it) once the pearl has been made into jewelry...other than by taking it to a lab.

 

[Bacca]

There's a mention of this technique in the GemologyOnline.com Forum. Maybe there will be additional information soon.

 

[Amrita]

The reason I asked this question is that a few months ago I bought some very nice nucleated freshwaterpearls wich I have realised that I would have had no chance to for sure distinguish from Akoyas if I did not know.

Unless you post a picture here, and let the experts give their opinion.. Of course, I am not referring to myself as I am still in the "learner" category, but there are really knowledgeable pearl people here..

However, this is a fascinating thread and if there were such a simple test, it would be so great.

 

[SteveM]

I think the amount of manganese in any water must depend on many different circumstances?

On this point it should be understood that it is not the manganese content of the water that is reflected in the pearls, rather the mollusk's metabolic expression of the relative presence or absence of salt/sodium. It's a slam dunk every time for the labs through spectrographic analysis. But you do need the instruments, and the ability to ammortize their expense.

If your FW look like Akoya (and yes, photos would be appreciated!) and you paid FW price, then just say hooray?as folks have been doing around here for some time.