Softer / Harder Pearls?

[Valeria101]

Heard once or twice that freshwater pearls are 'softer' than other cultured pearls.

Couldn't find any reference about such differences of any usual durability measure (scratch or breaking resistance) among nacreous pearls. In particular, other than noting the lower Mohs (scratch resistance) and over the top toughness of pearls in general, gemology publications yield nothing.

There's no lab in the house... so I am asking here: what is this all about?

 

[The Pearl Outlet]

Freshwater pearls are softer than Akoya, South Sea, and Tahitian pearls, and do scratch much more easily. This becomes very apparent when you drill a large number of pearls for setting. The cups on a pearl drill will easily mar a freshwater pearl, but will almost never mar one of these other types.

 

[pattye]

Hi All,

I,too, would like to hear more about this--funny it hasn't come up before!

Pattye
so many pearls, so little time

 

[Valeria101]

Terry, could this be because of the nucleii in the other pearls ?

Would assume MOP to be harder than pearls are... although you are talking about scratch resistence, so the outer layer is what counts.

 

[The Pearl Outlet]

I'd hate to venture just a guess. I'm betting someone like Gina Latendresse would have a great answer here.

I'll email her and see if she can shed more light on this.

 

[perlas]

I've noticed too that it's easier to scratch freshwater pearls compared to the south seas and tahitians.

Just don't know the hardness range of each pearl based on source specie.

Anyhow, checked below sites. Pearl hardness is said to be around 2.4-4.5.

http://www.gemsociety.org/info/gems/Pearl1.htm

http://gemologyonline.com/pearls.html

2.4 vs. 4.5 is a significant difference.

 

[Valeria101]

2.4 vs. 4.5 is a significant difference.

Hm... right. Not everyone likes to be reminded of either value... Fortunately, them pearls are tough

A bit of a paranthesis: At this point, I feel compelled to drop a note for the sake of any future reference to this thread: that this discussion is more theory than anything (would you agree?... ) because the Mohs is not quite as relevant for pearls as for the faceted gemstones for which it is more often mentioned. Because it does not capture toughness (resistance to breaking) and that does not go hand in hand with hardness (resistance to indentation or scratching) and wearability in pearls as it roughly tends to in jewelry stones - a seriously astounding property [LINK - thanks again, Caitlin!] due to their complex structure. Which means that all this does not make any news at all for pearl-wearing Paranthesis closed.

I'd hate to venture just a guess. I'm betting someone like Gina Latendresse would have a great answer here.

Awesome!

 

[perlas]

Right you are, Valeria!

If you tried roughly dropping, banging or hammering pearls, these beauts are mighty tough!

I'm sure you wouldn't even dare gently drop a nice emerald.

 

[Valeria101]

I'm sure you wouldn't even dare gently drop a nice emerald.

Drop? maybe just a little... haven't smashed any yet just by handling, with the implicit little shocks. Unfortunately, the most exercise my jewelry gets (and me, most of the time ) is typing - would that make the equivalent of a bull ride for a ring ?

It is a bit frustrating this 'hardness' debate about traditional jewelry materials with milenia of road-testing behind them. Everyone seems to want a single-number measure of durability and then complain that the result is too complicated (hardness, toughness, cleavage, chemical and fade resistance etc. combined, I mean).

 

[Valeria101]

BUMP for the original question!

 

[jshepherd]

Freshwater pearls are often described as more porous than other types of pearls.

The hardness of freshwater pearls when compared to other types of pearls is not something I have personally seen examined or contrasted. Cultured pearls, as you know, are 3.5 to 4.5 on Moh's scale. This is soft, but the platelet structure of the nacre makes them seem harder and more resilient.

Freshwater pearls have the thickest aragonte platelets of all cultured pearls, averaging more than 0.5-1.8. The thickness of the aragonite platelets correspond to the speed of nacre deposition which is influenced by species and location.

The akoya, for example, will only produce 0.15 mm per year in Ago Bay, but 0.3 mm on Kyushu Island (hence the thicker average nacer of akoya cultured in China). The average aragonite layer thickness corresponds to 0.35 to 0.5 microns, and a diameter of 3 to 6.

 

[GemGeek]

Durability varies a lot in freshwaters, but I have seen some pearls get scratched just by dragging one hank over another.

Freshwater pearls with better (harder, sharper, or more metallic) lustre seem to be more resistant to scratching - in my experience.

I am very curious also to know if anyone has hard data on this, as opposed to my anecdotal evidence

Cheers,
Blaire

 

[knotty panda]

I'm reasking this question, not so much about harder/softer pearls, but scratching. I think I've read a post or two where someone is skeptical about beading pearls next to metal beads. Has anyone really found significant pearl damage as a result of having a metal bead next to it? Thanks!

 

[Pearlgully]

I've strung high-end white round freshwater pearls next to 22k gold beads and I've never seen any scrathes on the pearls. Keep in mind that 22k gold is a soft metal. I would never put a "hard" metal up against a pearl.

When stringing metal beads with pearls, you should also make sure that the metal does not oxidize or rust.


Gail

 

[Sueki]

Hello Knotty,
Thanks for asking this.
Hello Gail,
What do you think about silver beads ?
I've got some rather nice Tahitians, and fancy silver for a change.
Or white gold, but the highest carat white gold I can find is 14 carat.

 

[Pearlgully]

Hello Knotty,
Thanks for asking this.
Hello Gail,
What do you think about silver beads ?
I've got some rather nice Tahitians, and fancy silver for a change.
Or white gold, but the highest carat white gold I can find is 14 carat.

I can only give you my opinion. As a goldsmith, I have experience working with metal but I am not an expert as far as the chemical alloys of metal. Having said that....the only silver bead I might use is one made of "fine" silver because it is soft. It could oxidize, though. Sterling silver in my opinion, is too hard and there are "other" metals alloyed in the sterling that I would not trust against high quality pearls.
I do not have experience with 14k gold but....I consider it to be a hard metal and I personally would not use it. Especially the white 14k gold, you never know what other metals they've alloyed in it (it could even be dipped).
Again, this is just my opinion. If you have inexpensive pearls and just want a pretty necklace.....all this really doesn't matter!


Gail

 

[knotty panda]

How interesting! Dfrey just posted a pic of one of Josh's high quality Tahitian keishis set in 14KT white gold palladium. Lovely to see.

 

[Pearlgully]

How interesting! Dfrey just posted a pic of one of Josh's high quality Tahitian keishis set in 14KT white gold palladium. Lovely to see.

That keshi pearl is in a setting, it is not moving or rubbing against the metal. In my previous post, I was specifically referring to metal beads.

Silver and gold beads are made in several different countries and as with many things these days, who knows what they are mixing in with the metal.


Gail

 

[Sueki]

Thanks for your thoughts, Gail.
Maybe I'll string some lesser pearls with silver and wait to see what happens...

 

[Pearlgully]

Thanks for your thoughts, Gail.
Maybe I'll string some lesser pearls with silver and wait to see what happens...

You are very welcome.

I just thought of this. If you don't mind possibly sacrificing one pearl, rub a bead against a pearl a little harder than it would rub in a necklace. If you see any damage.....then you already know the metal may scratch your pearls.


Gail