How Pearls Are Made

How Pearls Are Made

By Hoi Kiu Wong

Creator:mtulard | Credit: Unspalsh 

INTRODUCTION 

There is more to a pearl than what meets the eye; beyond its shiny appearance, have you ever wondered why and how pearls are even formed in the first place? Why do sea creatures such as oysters, mussels and clams create them? In this article, we will find the answers to these questions, and in addition to natural pearls, we will also be looking at the making of synthetic pearls. 

DIFFERENT TYPES OF PEARLS 

There are different types of pearls: natural, cultured and imitation. A natural pearl (also known as an oriental pearl) is formed naturally by an organism such as oysters, mussels or clams as part of their defence mechanism (details of pearl formation is in the next section How are they naturally made). A cultured pearl is also made by the same process; however, the irritant e.g. a plastic bead with a small piece of mantle, is purposely implanted into the soft tissue of the creature in order to artificially induce the secretion nacreous matter around the inserted nucleus - forming the pearl. As long as there are enough layers of nacre covering the irritant, a beautiful pearl will form. In regards to imitation pearls, they are completely different to the other two. Typically, the imitation pearl is a glass or plastic bead that is covered with a solution made from fish scales. This coating is thin and can eventually wear off over time [1]. 

Natural pearls can come from either salt or freshwater sources. It is found that pearls from saltwater are typically of higher quality than those from freshwater pearls. As we know, ideal pearls are perfectly round, but many have different, irregular shapes e.g. baroque pearls. Both natural and cultured pearls take many years to make - the mussels need to reach a mature age which takes approximately three years, and after introducing an irritant, it takes another three years for the pearl to reach a good size. Therefore, the formation of the perfect natural pearl is rare because in many instances, the irritant may be rejected or the shape of the pearl becomes too irregular; moreover, the oyster may die or have complications. At the end of a pearl’s life cycle which is up to ten years, only 50% of the oysters survive. Therefore, the prices of natural pearls can get very high as they are ‘accidental events’ so most pearls in the market are cultured pearls. Even so, farmers spend a lot of money trying to culture pearls, but not all of them will successfully form pearls that are soldable [1]. The most expensive pearl - 26 inches in length, 12 inches in width and weighing about 75 pounds, is valued at approximately $100 Million [6]. 

Fig. 3 The World’s Most Expensive Pearl 

Image Credit: Aileen Cynthia Amurao/SWNS.com [5] 

So, how can we distinguish between the different types of pearls? The easiest way to find out is by simply biting on it. Imitation pearls will glide across your teeth; on the other hand, the real pearl will feel ‘gritty’ as it is composed of many layers of nacre around it [1].

Fig. 1 Comparison between natural pearl and cultured pearl 

Image Source: Wikimedia Commons 

https://commons.wikimedia.org/wiki/File:Pearl_Section.svg

Note that there are other bivalve molluscs and gastropods that can produce pearls, but these are not made of nacre [2]. 

HOW ARE THEY NATURALLY MADE 

The formation of pearls (also known as moti stones) is a natural defence mechanism by marine oysters and freshwater mussels against irritants which could be anything from a sand particle, a parasite, to any foreign object that is present in the ocean. This mechanism is essential to these creatures as they are mostly bivalves, meaning that they have two valves (shells) that open and close. There is an elastic ligament connecting the two valves together, and the shells are often kept open so the oyster can eat - hence, it is easy for foreign objects to land on the organism’s  mantle, which triggers the formation of the pearl [5]. 

The mantle consists of multiple layers: the hard outer organic shell, the nacreous layer, the epidermis (nacre-secreting cells), a connective tissue and a ciliated epithelial layer. When an irritant enters and is located between the nacreous layer and the epidermis layer. Overtime, the epidermal cells of the mantle will secrete nacre (mother-of-pearl) that will surround the irritant; nacre is an iridescent material that is made of aragonite and conchiolin. Aragonite is a crystal form of calcium carbonate and conchiolin is needed to hold together the concentric layers of calcium carbonate together. Ultimately, this creates many nacreous layers around the irritant - forming the pearl [3]. 

Fig. 2 Stages in the formation of a pearl 

Image taken from: https://www.studocu.com/in/document/amity-university/bsc-biotech/lecture-notes/pearl-formation-animal-science/4680827/view 

CULTURED PEARLS

Cultured pearls are produced by human interference - where we would deliberately place a foreign object on the mantle so layers of nacre surrounds it, eventually forming the pearl (See Fig. 3). This is because natural pearls are very rare as it is an accidental process; therefore, most pearls in the market are cultured by ‘pearl farmers’ [5] - Today, more than 99% of all pearls sold worldwide are cultured [7]. 

Fig. 2 X ray of a cultured pearl 

Image Source: Hoanggiapearl I Wikimedia Commons 

https://commons.wikimedia.org/wiki/File:Bi_quyet_phan_biet_ngoc_trai_tu_nhien_va_nuoi_cay_1.png

There are a number of steps in the process of culturing pearls: The collection of oysters, the rearing of oysters, the insertion of the nucleus and harvesting. First, oysters are collected from the bottom of the sea by trained divers, and the best time to do this is two months into the summer season. Then, these collected oysters are cleaned and placed into rearing cages that are then placed into sea water hanging from the buoy. These cages protect the oysters from their predators and are placed in these cages for approximately 15 days, so that they can recover from the strain due to excessive handling and allow them to adjust to the shallow water conditions [5]. Once they have adjusted to the conditions, the harvested mantle tissue from an oyster is cut into small pieces. Another oyster is gently pried open and mounted in a stand to be operated on. A small incision is made so that the nucleus (foreign particle) can be inserted with a small piece of the mantle gland (from the first oyster). This second oyster is then placed back into the water to allow pearl formation. After a few months, the pearl is harvested, and if cut open, you should be able to observe the layers of nacre (albeit the layer would be thinner than that of the normal pearl) [7] . 

The most popular and effective method of culturing pearls are made from shells of freshwater river mussels from the midwestern states of the U.S., Canada and the Gulf of Mexico [7]. 

HOW ARE THEY SYNTHETICALLY MADE 

Artificial pearls are cheap imitations that are made of plastics, glass, fish scales and mollusc shell, and many chemicals are used to enhance its artificial lustre or its pearlescent substance is used to coat the bead to imitate the natural iridescence of nacre (mother-of-pearl) [8]. 

There are numerous different artificial pearls; for instance, the glass pearl, plastic pearl and shell pearls are beads made of their respective materials that is dipped or sprayed with pearlescent material (which is can be made from many different substances e.g. isinglass, fish scales, oyster scales, dyes etc.); the cotton pearl is made simply from cotton and mica, Bathed pearl has a mother-of-pearl core that is coated with a mixture of plastic enamel, lead carbonate, mica and titanium dioxide, then with a film of iridescent nylon. Moreover, corals are sometimes used to imitate pearls from pink conch, and hematite is used to imitate black pearls [8]. 

Fig. 2 Bracelet made of synthe

Image Source: DH gate I yoyozhen 

https://www.dhgate.com/product/high-quality-synthetic-pearl-bracelet-18k/264432849.html

BIBLIOGRAPHY 

[1] “How Pearls Are Formed.” Testing Meta Info, www.jthomasjewelers.com/pages/how-pearls-are-formed. 

[2] “How Do Oysters Make Pearls?” Natural History Museum, www.nhm.ac.uk/discover/quick-questions/how-do-oysters-make-pearls.html. 

[3] “Mechanism of Pearl Formation | Detailed.” YouTube, YouTube, 2 Jan. 2017, www.youtube.com/watch?v=t_h3tucvi3c. 

[4] AsapSCIENCE, director. The Creation of Pearls. YouTube, YouTube, 31 Aug. 2012, www.youtube.com/watch?v=NMXNf_sCFAA. 

[5] “Pearl Formation - Animal Science.” StuDocu, www.studocu.com/in/document/amity-university/bsc-biotech/lecture-notes/pearl-formation-animal-science/4680827/view. 

[6] Naas, Roberta. “This $100 Million Pearl Is the Largest and Most Expensive in the World.” Forbes, Forbes Magazine, 25 Aug. 2016, www.forbes.com/sites/robertanaas/2016/08/23/100-million-pearl-hidden-under-bed-sets-world-record-as-largest-most-expensive-pearl-in-the-world/?sh=72dcf579b0f2. 

[7] “Cultured Pearl.” Wikipedia, Wikimedia Foundation, 27 Jan. 2021, en.wikipedia.org/wiki/Cultured_pearl#:~:text=On%20the%20other%20hand%2C%20cultured,mother%2Dof%2Dpearl%22.&text=The%20mantle%20tissue%20is%20harvested,and%20cut%20into%20small%20pieces. 

[8] “Imitation Pearl.” Wikipedia, Wikimedia Foundation, 7 July 2019, en.wikipedia.org/wiki/Imitation_pearl#:~:text=A%20variety%20of%20methods%20are,nacre%20or%20mother%20of%20pearl.