Freshwater Vs. Saltwater

[Mikeyy]

Maybe the info is here and I missed it. I read where someone said Freshwater is more durable the Saltwater pearls. I was wondering if anyone had any actual information on this.
I have my own opinion on this and was wondering if there is any science available.
Personally I think Freshwater pearl nacre is lighter in weight then saltwater nacre. And so not as dense. But that is only my opinion. Does anyone know the facts on this?

 

[laurenb]

I think one of the engagement ring threads included a discussion about durability.

It'll be interesting to know if freshwater nacre is less dense. If so, I'll probably wash, rather than wipe, what I suspect are unusually acidic skin oils off mine more frequently.

I've always interpreted the durability comments as more of a nod to the fact that freshwater pearls will never wear down to a bead.

 

[SteveM]

Related comments that I recall off hand here involve water temperature and rate of nacre deposit (ie colder water, slower deposit, more compact and hard, more mirror, etc). I'm sure someone will be able to find the precise links. Freshwater durability related primarily to no eventual bead exposure seems correct.

 

[KAC]

Freshwater durability related primarily to no eventual bead exposure seems correct.

I think that is really where it stems from - I can't recall reading any actual studies.

Anybody have a rock tumbler and some time do an experiment?

 

[pearlescence]

Just from drilling them (so subjective) I reckon that some pearls are harder than others and some pearls have harder insides - or outsides- than their outsides - or insides.

 

[dkan 168]

Just from drilling them (so subjective) I reckon that some pearls are harder than others and some pearls have harder insides - or outsides- than their outsides - or insides.

I find Akoyas and Tahitians to be easier to ream to make the holes bigger than CFWP

DK

 

[Caitlin]

I agree with the concensus- CFWP are more durable because they won't wear down to the bead. Are you comparing solid nacre (natural) sea pearls and CFWP? I would think that nacre covered, fw mussel shell bead, pearls would not be comparable.

Or are the shells the same density as the pearls they produce?

While I am at it, how do pearly shells grow the outside layer of their shells? What makes it so dull?

 

[Mikeyy]

I agree with the concensus- CFWP are more durable because they won't wear down to the bead. Are you comparing solid nacre (natural) sea pearls and CFWP? I would think that nacre covered, fw mussel shell bead, pearls would not be comparable.

Or are the shells the same density as the pearls they produce?

While I am at it, how do pearly shells grow the outside layer of their shells? What makes it so dull?

It doesn't seem that it would be that hard to test really.

 

[Caitlin]

Does that mean you will do it?

 

[AMc]

Excellent and intriguing question... From my pearl studies I learned the reason why FW Mussel shell is used as the bead is because the shell has the same specific gravity as the nacre, which means that the bead inside reacts i.e. expands and contracts, at the same rate as the nacre in response to external temperature changes. This is why the famous Chinese "Fire Balls" are essentially a bad idea (besides the fact that the bead material originates from an endangered species ), the specific gravity of the bead is denser than that of the nacre, and eventually cracking and splitting of the surface can occur if exposed to extreme and quick temp changes.

It's my thought that FW is very much more durable than your typical Akoya saltwater pearl- much less sensitive to wear and tear and nacre erosion at any rate- mainly because of their solid crystalline composition... I haven't read anywhere that saltwater nacre rates any higher on the Moh's Scale (4/Talc) than that of Freshwater, although admittedly saltwater nacre contains an additional trace element (I am pretty sure it's magnesium, but I'll have to double check) that is found mainly in FW shell which in theory could make it "harder" than that of a Freshwater pearl- in addition to Mikeyy's comment about the colder water leading to denser platelet layers (good one!) and brighter shine. But on the other hand, I have seen some gorgeous FW rounds and baroques that would make Akoya farmers weep with envy.

I would definitely be interested in hearing about any experiments done and your conclusions, but until then, my money is on the Freshwater pearl.

 

[AMc]

While I am at it, how do pearly shells grow the outside layer of their shells? What makes it so dull?

Hi Caitlin,

I should have put this in with my earlier response. The outside part of the shell is the beginning of the entire adult oyster. The baby spat develop what is called an "umbo" first which is the rounded or ovalish shell growth that protects the soft body once the baby attaches to it's perch (rock or whatever). The outer layer grows first (although in concurrence with the pearly layer on the inside), and is composed of conchiolin which is that organic "glue" we can also find between nacre layers in a pearl holding the aragonite platelets together, and keratins (the stuff fingernails and hair are made of) in tightly woven layers. All the bumps, ridges and whorls that are visible on the outside of the shell are responses to outside stimuli such as temp changes, current fluctuations and predator attacks (sounds very scary!). I forget what they call the actual outer layer, but for some reason the word Umbo has stuck with me. It's so cute. Umbo.

 

[Caitlin]

Thanks, great post!

If fw mussel shells are the same specific gravity as salt water pearls are they the same specific gravity as freshwater pearls too? An a=b=c therefore a=c, kind of thing?

Maryd, I think the bead material is tridacna shell.

 

[AMc]

Hi Maryd,

The bead material used for the Fire Balls is shell from strombus gigas, the Giant Clam.

 

[AMc]

Oops- Lol! I got the shell name wrong!

Caitlin is correct- it's T. gigas

A=C sounds like a solid theory, but I'd like to consult Strack before I make any concrete statements. I don't remember reading about any measurable amounts of magnesium found in the Freshwater pearl itself, just it's shell (maybe the important magnesium is found in the outer and middle layers of the hinge where material is thickest and most concentrated?)... but I will definitely do some homework and let you know!

 

[Caitlin]

saltwater nacre contains an additional trace element (I am pretty sure it's magnesium, but I'll have to double check) that is found mainly in FW shell which in theory could make it "harder" than that of a Freshwater pearl-

There is a trace element in fw shell (but not pearls) that matches one in salt water pearls, but not in salt water pearl shells?

I wonder what the argument is for (or against) using pinctada shell beads....I think Josh does that.

 

[AMc]

I'm pretty sure you're correct about Josh, which I think is a wonderful idea- recycling at it's core In addition to the trace mineral amounts (I'm reading it's manganese, not magnesium, sorry bout that!), American FW Mussel shell is a preferred medium for nuclei due to it's whiteness and density... maybe margaritifera shell is more brittle? We'll have to pose the question to him, although I do know that farmers and technicians prefer totally white shell for Akoya culturing, and beads that show colored strata are generally considered fine for darker pearls, or pearls that are destined for thick nacre layers since the discoloration won't show through.

I see from Strack that the specific density of a natural saltwater pearl ranges between 2.6 - 2.75, and a cultured pearl measures 2.72-2.78, so the presence of a bead nuclei doesn't seem to make the pearl all that much more dense, although Strack mentions that the composition of the mineral content in the pearl does play a factor such as too much conchiolin, which can make for a dull, greyish cast. Interesting stuff

 

[Caitlin]

You are better at getting around Strack. Always great to mention material from Strack for those who don't have a copy!

 

[Nerida]

what percentage of the CFWP that are nucleated are using the T. gigas shell? Most traders I know deny the use of this (not surprisingly) - obviously some do, but I wonder if there is any evidence to suggest how many? And what other shell is used?

I would assume many of them use the FW mussel as is used for the SS industry...?

 

[Caitlin]

Mussel nuclei that size , if procurable, would be very expensive. I think these are the nuclei Strack talked about, which appear to be in production now. The nucleus is made of shell powder and a chemical glue formulated specifically for this use. It that yields a perfectly smooth surface that nacre loves to coat.

 

[KAC]

I would assume many of them use the FW mussel

I doubt it, I think most probably use the T Gigas. This is china remember, using T. Gigas is peanuts compared to the lead paint and tainted baby food problems we've seen.

The nucleus is made of shell powder and a chemical glue formulated specifically for this use.

Caitlin have you heard of any farmers actually using this nuclei?