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LuxeSci Show Notes: S1E16: Pearls

Hello and welcome back to LuxeSci.  I’m Dr. Lex and this is Dr. Dimos. This week we’re taking the jewels of the sea, pearls!

Dimos - what have you always wondered about pearls?

Alexis - I’ve always wondered exactly how pearls are made by oysters, hopefully you’ll answer that with the background 

Mikimoto pearl culture process was patented in 1916

Dimos - have you ever bought pearls? I’m going to tell a little story that may feel like deja vu.  When I travel, I think to buy a little piece of jewelry as my souvenir in addition to the gifts I pick up for others.  I love it because when I wear the pieces, I have a story that goes with each one. One of the whirlwind trips I did for work involved flying from the West coast to China and then from China to Bangladesh to meet with grantees and then from there to Dubai and back to the West Coast, a true around the world trip.  When I was in Bangladesh I visited a market, as is my habit, and I found some gorgeous black pearls.  They are called black pearls but they really appear more deep purple.  Perhaps Dimos you will cover the difference between white and black pearls and other colored pearls?

Dimos - First of all we need to ask: what Mollusk groups create Nacre: Well there are 8 groups from completely different parts of the world:

Nautilus pompilius, Haliotis iris, Haliotis rufescens, Bathymodiolus azoricus, Atrina rigida, Lasmigona complanata, Pinctada margaritifera, and Mytilus californianus.

A paper from the american chemical society shows evidence that environmental temperatures are directly related to nacre crystal misorientations in pearls and that pearls can be used as a paleo-thermometer to be able to study climate change.


Architecture uses

Both black and white nacre are used for architectural purposes. The natural nacre may be artificially tinted to almost any color. Nacre tesserae may be cut into shapes and laminated to a ceramic tile or marble base. The tesserae are hand-placed and closely sandwiched together, creating an irregular mosaic or pattern (such as a weave). The laminated material is typically about 2 millimetres (0.079 in) thick. The tesserae are then lacquered and polished creating a durable and glossy surface. Instead of using a marble or tile base, the nacre tesserae can be glued to fiberglass. The result is a lightweight material that offers a seamless installation and there is no limit to the sheet size. Nacre sheets may be used on interior floors, exterior and interior walls, countertops, doors and ceilings. Insertion into architectural elements, such as columns or furniture is easily accomplished.[citation needed]

Musical instruments[edit]

Nacre inlay is often used for music keys and other decorative motifs on musical instruments. Many accordion and concertina bodies are completely covered in nacre, and some guitars have fingerboard or headstock inlays made of nacre (as well as some guitars having plastic inlays designed to imitate the appearance of nacre). The bouzouki and baglamas (Greek plucked string instruments of the lute family) typically feature nacre decorations, as does the related Middle Eastern oud (typically around the sound holes and on the back of the instrument). Bows of stringed instruments such as the violin and cello often have mother of pearl inlay at the frog. It is traditionally used on saxophone keytouches, as well as the valve buttons of trumpets and other brass instruments. The Middle Eastern goblet drum (darbuka) is commonly decorated by mother of pearl.[citation needed]


Biomedical use[edit]

Further information: Pearling in Western Australia

The biotech company Marine Biomedical, formed by a collaboration between the University of Western Australia Medical School and a Broome pearling business, is as of 2021 developing a product nacre to create "PearlBone", which could be used on patients needing bone grafting and reconstructive surgery. The company is applying for regulatory approval in Australia and several other countries, and is expecting it to be approved for clinical use around 2024–5. It is intended to build a factory in the Kimberley region, where pearl shells are plentiful, which would grind the nacre into a product fit for use in biomedical products. Future applications could include dental fillings and spinal surgery.

Regarding the type and color of pearl producing oysters from Wiki:

Pinctada maxima produces South Sea pearls in colors ranging from white, silver, champagne, gold. Pinctada margaritifera produces South Sea pearls commonly referred to as Tahitian pearls or black pearls which in fact come in color hues including gray, platinum, charcoal, aubergine, peacock. Currently south sea pearls are cultured primarily in Australia, Indonesia, Tahiti and now, the Philippines. Because these pearl oysters are so large, a much larger nucleus than usual can be used in culturing.

Nacre is iridescent because the thickness of the calcium carbonate layer is similar to the wavelength of light. Light reflected from the outer surface is therefore able to interfere with light reflected from the inner surface. Constructive and destructive interference of different wavelengths of light produces different colors when viewed at different angles of incident light.

Recently, research has demonstrated that diffraction plays a major role in creating iridescent color effects in mollusk shells. By using a scanning electron microscope (SEM), the surface of a French Polynesian abalone shell was found to have a fine-scale diffraction grating structure. In addition, stacks of thin crystalline nacreous layers or platelets were found below the surface.


  • I dove into a review article (of course) to discover the biomedical applications of pearls (Loh et al Materials, 2021). There are some interesting biomedical applications for pearl powder, an ingredient that has been used in Chinese Medicine for thousands of years.  

  • Since pearls have a dense protein and mineral content

  • The main component, as you’ve said, is calcium carbonate

  • This can exist in three polymorphs depending on conditions: calcite, aragonite and vaterite

  • Aragonite - main inorganic component of luster

  • Vaterite pearls - lack luster (surely the origin of the saying) and result from irregular biomineralization of the CaCO3

  • To make pearl powder, the most common method is the decalcification (removal of calcium or calcium compounds usually from bone or soil) by disodium etyhlenediaminetetraacetate. 

  • This may undermine the structures and therefore the role of proteins found in the pearl powder

  • Gas diffusion is another option that can separate pearl powder from nacre powder

  • On to the uses of pearl powder:

  • Wound healing - very few therapeutic agents available for stimulating wound healing

  • Wound healing has three phases:

  • Inflammation - release of elastases and proteases by neutrophils - one of the first white blood cell that comes to a site of infectin or injury. It can phagocytose or eat other cells leading to vascular dilation and increase blood vessel permeability (so things that are needed can get to the wound site fast)

  • Proliferation - skin cells come to the site to promote wound angiogensis (formation of new blood vessels)

  • Maturation - other skin cells produce the extracellular collagen matrix required to stitch your skin gack together

  • Studies done in rats and human wound healing models (human skin cells in culture that are disrupted) have shown that the nacre and pearl extracts cultivated well-vascularized tissue and improved ECM production and was able to promote migration of new skin cells to injury sites.

  • The hypothesis is that a protein named conchiolin is responsible for pearl’s skin healing and improving qualities

  • This is taken as gospel in the beauty world where pearl powder is added to skin care products

  • This has not been substantiated by science though. And experiments to date with nacre, pearl powder or pearl extracts have only been done in animal studies or in vitro human skin experiments

  • Of course i’d be remiss if i didn’t include some nano technology here, as we’ve seen it with almost all our other precious gems.

  • A study conducted by Chen et al saw hastened wound closure and improved biomechanical strength of recovered tissue in a rat skin excision model for both micro and nano-szied pearl powders

  • While this field requires more study, the authors do envision a product that would consist of an antimicrobial nanofibre dressing with pearl powder that could protect injured tissues from pathogens and stimulate tissue regeneration.  This would be a huge boon for burn treatment. And just to point out here that while pearls for jewelry are quite expensive, cultured or natural, the fact that pearls can be cultured, and done so sustainably means that it’s not as expensive of a material as some of our other podcast subjects

  • Since the topic i wondered about at the beginning of the episode was the color pearls, I found this really interesting article about the structural colors of pearls (i’ll post some of the figures on our instagram) 

  • This is by Ozaki et al and was published in Nature as a scientific report in 2021

  • As we’ve said, luster is perhaps the characteristic that most defines pearls and is produced by periodic structures of aragonite crystals and conchiolin sheets. 

  • This is defined as a structural color = one that originates from multiple reflections in a nanolayered structure of nacre (mother of pearl)

  • The thickness of the layers determines the color reflection from the nacre

  • Other examples of structural colors include: future podcast subject, opals, morpho butterflies, jewel beetles and pollia fruits (i had to google that last one and it’s a beautiful fruit that looks like a raspberry with the individual fruit bulbs being a round, shiny black-pearl colored sphere and the structural coloration is the most intense of any known biological material

  • So how’s that for a tangent?

  • Now for another one, the study of these reflections from multilayered structures is not purely academic, these optical elements (thin-film interfaces or multiple reflections) have been used in spectrometers, lasers, optical filters and other devices.  We’ve even mentioned them in earlier podcast episodes (Plaid) when referencing gratings

  • Now finally back to the pearls - pearls are graded by size, color and luster, etc

  • Obviously pearl manufacturers would want to control the color of the pearls and since that has to do with the thickness of the aragonite crystal layer, the authors of the study developed a nondestructive method for doing just that for Akoya pearl farming - which is pearl farming using the small Akoya oyster and they are said to be some of the best cultured pearls

  • This nondestructive method is essentially an optical model, which means it uses data to predict what is happening with the pearls, specifically internal light scattering and its transmission. 

  • Fortunately for the authors, the transmission and reflection spectra of the pearls calculated showed good agreement with the experimental results

  • If this method is reproducible, i have a feeling those authors could make a lot of money with this method


  • Nucleation - The addition of a foreign substance that can trigger a formation of material around it

  • Nacre - mother of pearl

  • Luster - gentle sheen or soft glow, especially from a partly reflective surface

  • Decalcification - removal of calcium or calcium compounds

  • Neutrophils - white blood cells that are early harm sensors and actors

  • Angiogenesis - blood vessel creation

  • Structural color - when the color of an object is dictated by the reflection of multiple layers of itself (cause i’m so shiny)

Cocktail party facts:

(Dimos will discuss cost vs. cross-sectional area graph) 

  • What is the probable origin of the term lack luster - type of pearl where the biomineralization of CaCO3 was imperfect (aka vaterite pearls) - supposedly first heard in Shakespear’s As You Like It

  • Claims of pearl powder’s amazing skin healing properties aren’t back up by enough science to be conclusive as of yet (in case a party goer is trying to sell you on the latest crazy expensive skin cream you just have to try), goes for gold or diamonds too

  • How do pearls get their color: color of the lip of the oyster and pigments within the conchiolin.  They can also be dyed so watch out for fakes (this fact courtesy of a diamondbuzz blog post that I linked to on our Instagram account)

Whelp, you’ve done it, spent another 20+ minutes with Dr. Dimos and I and the beautiful and enchanting pearls.  We hope you remember a little cocktail party fact about pearls then next time you see someone wearing them, or a skin care product purporting miracles because of them.

A very special thank you to my cohost and audio engineer Dimos.  Our theme music is Harlequin Moon by Burdy.  If you like us, please, please, please subscribe and rate us wherever you listen to your podcasts.


Check us out on Instagram to see Dimos' graph:


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