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Pearl Nacre

Pearl Nacre Guide

What is Pearl Nacre?

Nacre is exactly what the title of this page implies: it is the building blocks of a pearl’s beauty.

Nacre (aka mother-of-pearl) is the organic crystalline substance that mollusks produce to create the interior of their shells and protect themselves from irritants and parasites by smoothing them over with this substance and eventually creating a pearl.

What is Nacre?

Nacre is the crystalline substance that both makes up a inside of a mollusk’s shell, and also is used to create pearls. Pearl nacre is known for its glossy luster, brightness and subtle rainbow iridescence.

Nacre is a mixture of calcium carbonite (CaCo3) and a biological, organic binding agent named conchiolin which “cements” the crystalline platelets together.

The calcium carbonate consists of microscopic crystalline aragonite platelets that are roughly hexagonal in shape. The CaCo3 and conchiolin is secreted continuously to form strong, semi-transparent layers around the pearl’s nucleus. Scientists liken this structural arrangement to a brick wall, and at the same time, layered like an onion.

Transparent Nacre Crystals Diagram

Nacre crystals look roughly like semi-transparent hexagons. When stacked and layered together, light traveling through the layers and bouncing back to your eye at various wavelengths creates the phenomenon of iridescence.

How Nacre Creates Strong, Beautiful Pearls

To create a pearl, mollusks will capture an irritant within a sac (known as the pearl sac). It then begins to secrete liquid nacre continuously around the irritant inside the shell (usually a parasite or bit of flotsam and rarely, grains of sand as the legend holds). The nacre smooths over this irritant and makes it so that the mollusk does not get its soft insides damaged by the intruder. The result over a period of years is a precious pearl.

The thicker that the nacre layers are, generally the more beautiful the pearl will be. Its chances of showing sharp, highly reflective luster are increased, and its ability to refract subtle rainbow iridescence is also enhanced with thicker nacre layers.

Not only does thicker nacre layers make for more beautiful, valuable pearls: it also makes pearls incredibly strong and resilient. While pearls are easily scratched - measuring a mere 3 on the Moh’s Scale which is equivalent to Calcite – they are amazingly strong, able to withstand surface strikes without cracking extremely well. Pearls with thick nacre layers are more durable and able to tolerate wear and tear – the thicker the nacre, the better the pearl.

 

Pearl Nacre Under Microscope

This electron microscope image of nacre showcases the layered structure of aragonite platelets and the conchiolin “glue”. Cultured pearls can contain thousands of microns-thick layers of nacre. Photo courtesy of Science Mag.

Cultured Freshwater pearls are made of 100% solid nacre; the pearl’s nucleus is just a tiny piece of donor mantle tissue, not a round mother-of-pearl bead like its saltwater cousins. As the pearl grows inside the Freshwater mollusk, the tiny square of tissue degrades inside the structure, leaving a pearl with a solid core of nacre … very much like the composition of a natural pearl.

This solid crystalline nacre make-up of Freshwater pearls make them very, very durable.

How Nacre Creates Luster

Pearl nacre is a key component of the attribute that makes pearls valuable as a precious gemstone:  LUSTER.

Luster is created when light strikes the surface of the pearl and rebounds back towards the observer, giving the viewer a bright, shiny and reflective pearl surface to admire.

Luster is also what gives pearls the soft glow that appears to come from inside. This occurs because light waves penetrate the surface layers of nacre, travel to the pearl's interior and then bounce back through the layers of crystal to the viewer, embuing pearls with a gorgeous inner glow.

Luster is graded by evaluating the details of reflected objects seen on the surface of the pearl, AND the crispness of the edges of reflected light sources visible on the pearl. The sharper and more detailed the reflected objects are, the better the luster is. Reflected light sources should have crisp, sharp edges with as little fuzziness as possible.

Different pearl types display different rates of luster, which corresponds to the average depth of nacre surrounding the internal nucleus. The tighter and more compact the nacre layers are, the faster the light return will be, creating sharper, crisper luster with defined reflections.

Cultured Akoya pearls are famous for their bright, “mirror-like” luster that is incredibly sharp and detailed.

Akoya pearl luster is also commonly described as "ball-bearing" luster, as these pearls typically have a hard, almost metallic shine.

The cold waters of the oceans in Japan act to slow the oyster’s metabolism, which causes the mollusk to produce nacre more slowly in tightly compacted layers around their mother-of-pearl bead nucleus, creating that trademark glossy shine.  

Akoya pearls have the thinnest nacre layers of all cultured pearls, measuring 0.6mm and under for most. The tightly compacted crystal makes up for that however, by gifting these pearls with the brightest, most reflective luster of all cultured pearl types.

Akoya Pearl Luster
Tahitian Pearl Luster

Larger cultured pearl types like Tahitian pearls have what’s often called “satiny”, softer luster.Reflected light sources may have very slightly blurred to very blurred edges, and reflected objects in the pearls’ surfaces can appear softer and less detailed than that of the Akoya.

Very high quality Tahitian pearls (AAAA/Gem Quality) can come close to an Akoya mirror-like shine ... but these are usually created by younger oysters with a higher metabolism rate, and are most often seen in the smaller pearl sizes under 11.0mm.

Tahitian pearls are cultured in the warm, tropical waters of the French Polynesian islands, so their nacre layers are not as tightly compacted as that of the Akoya. Minimum nacre depth measures 0.8mm around the pearl nucleus.

White and Golden South Sea pearls are also famous for their “satiny”, more touchable luster.

While not always the case, South Sea pearls typically display softer, more diffused edges on reflected light sources, and somewhat blurred reflections visible on their surfaces. Very high quality South Sea pearls can approach the high rate of reflectivity of Japanese Akoya, but this rare and usually only seen in the highest caliber pearls.

These pearls are also cultured in warm, tropical waters of the Philippine Islands and Western Australia, and so the oysters layer nacre more quickly, with a slightly looser crystalline arrangement than the Akoya.

Their extremely thick nacre layers average between 2.0-3.0mm thick, so while the sharpness of the luster may not be "mirror-like", South Sea pearls often possess a beautiful, ethereal glow, and long-lasting durability.

South Sea Pearl Luster
Freshwater Pearl Luster

Freshwater pearls are the ONLY cultured pearl type that is 100% solid crystalline nacre. This means that light takes longer to travel through the layers before returning to the viewer, which creates a softer, satiny luster for this pearl type.

The edges of light shining on the surface of the pearls will typically be diffused and somewhat fuzzy. Objects and people reflected in the surfaces will not be completely recognizable, and you may not be able to see certain facial features such as your eyes or your smile. Metallic Freshwater pearls are the exception to this rule, and mimic the Akoya with their glossy, metallic luster but they are rare, accounting for just 1 in 3,000 pearls.

Freshwater pearls also often display that beautiful inner glow unique to pearls; the finest Freshwater pearls can look like milk glass ... nearly transparent in certain lighting conditions and with careful observation.  


How Nacre Creates Orient

What is Orient?

Orient is a combination of luster plus iridescence. This beautiful visual phenomenon is unique to pearls; no other gemstone in the world displays orient … they may display iridescent effects, but not orient. Additionally, not all pearls display orient – it is a rare visual effect that belongs only to the highest quality pearls.

Orient is different from the primary body color and secondary overtone colors pearls possess. For example, a pearl can have a white body color, a pink Rose overtone, and rainbow orient shifting and shimmering on top of that. This rainbow iridescence appears to float over the surface of the pearl.

So how is Orient created?

As explained earlier, pearls are layered with hexagonal semi-transparent aragonite platelets and conchiolin “glue” … But many of these layers are incomplete. They are uneven and overlap each other in layer upon layer.

Pearl surfaces viewed under microscopes reveal landscapes that appear almost scaly – in fact, this is a major reason why the Tooth Test works so well in determining whether a pearl is genuine or synthetic! That rasp you feel when scraping your teeth upon a pearl’s surface IS all these varying layers of crystal.

This “scaliness” is part of every single microns-thin layer of nacre all the way down to the pearl’s nucleus.

This delicate tracery of crystal can be thought of as the pearl’s individual fingerprint … no two pearls can ever be exactly the same.

Take a look at the slideshow below to get an idea of what I mean.

Abalone nacre as seen under a high-powered microscope. Note the uneven, scaly texture, and the unique topography of the gem’s surface.Photo courtesy of Dimitri Becue

Scientists using an electron microscope were able to get incredibly detailed images of what a pearl’s surface looks like at the nano scale …Notice the hexagonal shapes of the aragonite platelets, the scaling and swirling textures. Amazing.

Photo courtesy of Research Gate.net

Pictured here is a Tahitian pearl under high magnification showing the uneven layers of nacre. Photo courtesy of GIA.org

Ok, so that is pretty neat … But why does ANY of this matter, and how does it relate to that gorgeous visible phenomenon of iridescent orient?

Because it is these scaled, uneven, layered topographies that creates iridescence!

We all know that a single beam of light can be broken up into the seven spectral colors of the rainbow using a prism.

Prism

 

That’s essentially what pearls do.

Beams of white light hit the crystalline topography of the pearl’s surface; and most of that white light beam continues past the top layer and works its way through the pearl’s interior layers, finally hitting the solid bead nucleus inside and returning to the viewer.

BUT parts of that beam hit the crystalline platelets and then refracts into the seven prismatic colors of the rainbow, creating orient for the pearl’s observer.

The uneven, scaly surface layers of the pearl provides the perfect medium for breaking up light beams and refracting various colors at different color wavelengths.Each crystalline platelet acts like a miniature prism, breaking up the beam of white light into a rainbow.

The aragonite platelets’ transparency and thinness (measuring in the microns) makes the transmittal of light and the light beam’s refraction possible.

How Pearl Nacre Creates Orient

This diagram is a simple representation of how white light striking and passing through the layers of crystal creates rainbow iridescence.

Some pearls display orient at a much stronger rate than others … For example, the uneven shapes of Baroque pearls have a much easier time refracting light at various wavelengths than the smoother surfaces of the perfectly symmetrical pearls.

Baroque pearls have irregular surfaces, with some areas consisting of densely compacted crystal, and other areas having thinner nacre layers.

Baroque Pearls Display Stronger Rates of Orient

These naturally-colored Baroque Akoya pearls are perfect for showcasing what intense orient looks like. The irregular compaction of the nacre layers that occurs with Free-Form Baroque shapes encourages and enhances this iridescent effect.


Thin Nacre vs. Thick Nacre Pearls

By now we know that thicker nacre makes pearls more beautiful, more lustrous and gives them a better chance of displaying orient. But thicker nacre also makes pearls stronger and more durable.

Pearls with thicker nacre layers are more able to withstand daily wear and tear, and resist chipping or peeling around the drill shafts.

Thin Nacre Creates Chipped Pearls

Major chipping and wearing away of the nacre layers exposing the bead nucleus inside these Akoya pearls. These pearls were improperly knotted, causing major damage to the vulnerable areas around the drill shaft, but you can also notice some of the pearls with very thin nacre layers just wearing away.

This section will deal primarily with saltwater Akoya pearls because Tahitian pearls have a minimum nacre depth of 0.8mm before qualifying for export, South Sea pearls generally have an average of 2.0-3.0mm of nacre depth and Freshwater pearls are (with some new exceptions) solid nacre. So really it is Akoya pearls that you’ll primarily need to look out for in this area.

Akoya Pearls with Thick Nacre

These cultured Akoya pearls display thick, lustrous nacre layers – the glow and depth of these pearls is obvious to anyone who sees them.


Akoya pearls with thin nacre can still appear shiny, but they lack depth and glow. So that’s really what you are looking for when you want to identify thin-nacred pearls, barring inspecting the drill holes of the pearls which can be difficult to do.

Pearls with thin nacre can also appear shadowed – you’ll want a trained eye in order to be tell for sure, but the interior bead nucleus will show through the thin nacre layers and tinge them white, tan or yellowish color.

This example shows pearls that appear “too” white with a very hard shine – the pearls are almost plastic looking. The white mother of pearl bead nucleus is too close to the pearl surface.

Akoya Pearls with Thin Nacre

Another tell tale giveaway for thin-nacred pearls is “blinking”.

Blinking happens when the bead nucleus inside flashes under strong lighting conditions. The flashes are usually light flares – yellow and orange are most typical.

Blinking occurs on Akoya pearls with thinner nacre layers; on AA and AA+ Quality strands, one or two pearls may display blinking but AAA Quality and Hanadama Akoya pearls will never show this phenomenon.

This triple strand Akoya necklace features TONS of blinking and thin-nacred pearls. Notice that the pearls are very “shiny” but lack any depth or inner glow. Again, the pearls look almost like plastic.

Many of the pearls here are so thin-skinned that you can see the nucleus easily, but I have pointed out some blinking that I noticed.

 

You’ll almost never see these kinds of defects with Akoya pearls that have been allowed to acquire thick, lustrous nacre over an appropriate period of time in the oyster.

Thick-nacred pearls will appear bright and shiny, but not flat in color or appearance; Akoya with thick nacre layers appear to almost glow from within, with gorgeous complexity in terms of color and how the pearls react to light.

Hanadama Akoya Pearls with Thick Lustrous Nacre

This stunning strand of Hanadama Akoya pearls features clean, thick nacre that exudes a wonderful glow.

What Are The Best Pearls To Buy?

We love all of them! Each of the pearl types has something to offer pearl lovers of all stripes.

Both White and Golden South Sea pearls feature gorgeous natural colors, the largest pearl sizes and the thickest nacre of all but can get expensive.

Freshwater pearls are solid nacre, but getting your hands on a strand of perfectly round pearls with mirror-like luster is difficult. The vast majority of these pearls are going to be very slightly off-round to off-round in shape, with softer, more satiny luster levels.

Black Tahitian pearls are a fantastic choice for pearl enthusiasts who want pearls that are totally unique and naturally black in color.

… But let’s say you’re looking for a classic white pearl necklace for under $1500, then that leaves us with Freshwater vs Akoya pearls.

Choosing the best pearls depends on a variety of factors like Luster, Price and Quality as well as personal factors such as perceived value and your own aesthetics.

Cultured Freshwater pearls are generally a more “casual” pearl option. These pearls have lower prices – usually a quarter to a half the price of the saltwater Akoya – solid nacre composition and higher durability and more variation in shape, and a softer, more touchable luster.

I usually recommend Freshwater pearls for shoppers with a smaller budget but who still want that classic pearl look.

Japanese Akoya pearls are the more luxurious, high-end option for pearl shoppers. These pearls will be perfectly round in shape, with highly reflective, mirror-like luster and that definitive Mikimoto pearls look.

To ensure that the Japanese Akoya pearls you purchase have the thickest nacre layers possible, I HIGHLY recommend shopping our Certified Hanadama Akoya Pearl Collections for both necklaces and earrings.

Hanadama Akoya are independently certified by the Pearl Science Laboratory of Tokyo, Japan as having the thickest nacre layers of all Akoya pearls, the best luster and shimmering Orient (which they term Aurora effect).


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