PEARLS
(Singular nouns:  Fr-perle; Ger-Perle; Nor-perle; Rus- перл / жемчуг)




A. Pearl. Source of this pearl, apparently cultured, was not divulged (diameter - 8.5 mm).  Commercial Mining.   photo by Jeffrey A. Scovil)
 


B. Pearls. Three strands of diversely colored, but well sized cultured pearls.  M. Freeman.   photo by Jeffrey A. Scovil)




C. Pearls.  This French Polynesia stamp (66 francs, dated 14 June 1995) features two black pearls from Tahiti.  photo of stamp by Richard Busch, reproduced by permission http://mineralstamps.rbnet.net)  

DESCRIPTION:  The following description relates to natural and cultured pearls formed in molluscs within either marine or fresh-water environments:   Aragonite (CaCO3), the chief constituent of the concentric layers of most pearls, makes up about 90 per cent of typical pearls;  the remainder is chiefly conchiolin, "a Gluelike protein that binds together the calcium carbonate" (Dubin, 1987, p.297), plus or minus up to two per cent water and traces of, for example, magnesium, sodium and strontium.  Some pearls include or consist largely of calcite (another CaCO3 polymorph) along with or instead of aragonite.   Microscopic studies indicate the constituent calcium carbonate crystallites to occur as radiating prisms, whichever polymorph (or even if a combination of polymorphs) is present. 
     Colors - white or off-white, commonly bluish or yellowish;  also reddish, pink, yellowish, golden, orange, greenish, blue, lavender, brown, bronze, black and gray;  and, some "white pearls" exhibit relatively light hues of one or more of the other colors as overtones.  The term orient, which is used widely to describe the subtle play of color exhibited by pearls, is frequently modified by an indication of the predominant overtone -- e.g., rosé orient.  Attention is directed to the brief definitions of colored pearl and fancy pearl given under OTHER NAMES.
    H.  2½ - 4½ ;   typically  3½ - 4. 
    S.G. 2.61-2.85, which differs with such things as mollusc host, locality and even color of pearls within the same area -- see Tabulation given as an Addendum to this entry.  Despite the values shown on the table, a specific gravity of greater than 2.75 is used widely as a general criterion to distinguish pearls as cultured rather than natural.  However, in my opinion, considering the range of recorded values, it seems only prudent to recommend to anyone who considers it important to distinguish between natural and cultured pearls that (s)he not use this criterion.  Instead, contact an expert who has the required instruments to make a definitive distinction. --  Instruments and procedures have been devised whereby natural and cultured pearls can be distinguished from each other.  See also the statements about the densities of simulated pearls under SIMULANTS.
    Light transmission - semitranslucent to opaque
    Luster - pearly to submetallic (The fact that the quality of a pearl's luster correlates with the quality of its surface is widely recognized.)
    Breakage - uneven
    Miscellaneous - Most pearls exhibit an iridescence (abalone pearls commonly exhibit a particularly striking one);  effervesce with dilute HCl;  and feel gritty to cutting edges of teeth.  This last characteristic appears to relate to the texture of pearls, which may be described as serrated, as distinct from that of most simulated pearls, which Webster (1958) characterizes as looking "like a blotting paper."   Also, I have been told that pearls from marine oysters fluoresce white whereas those from freshwater mussels fluoresce yellow. -- To date, however, I have been unable to check this claim
        Shells of the mollusc hosts of pearls are commonly distorted or relatively small because of their abnormal histories.
       
So-called porcelaneous (i.e., non-nacreous pearls) have been found in several molluscs -- e.g., Baler shells (Melo melo Lightfoot, J. in Solander, 1786), horse conchs (Pleuroploca gigantea Kiener, L.C., 1840), pink queen conch (Strombus gigas Linnaeus, 1758), the giant/gigas clam (Tridacna gigas Linnaeus 1758) and lion's paw scallops (Nodipecten nodosus, Linnaeus, 1758) -- see, for example, Koivula et al. (1993, p.294) and Moses et al, (1999, p.140)I suspect that non-nacreous pearls have also been produced by at least some molluscan species, widely known to produce nacreous pearls, as a consequence of their having atypical physiological makeups and/or living in particular environments.  And, as I unhappily learned as a child, if a pearl is found in an oyster after the oyster has been cooked, the pearl no longer exhibits a pearly luster.  

OTHER NAMES: Scores of designations, that consist of pearl preceded by an adjective or modifying noun, have been applied to both natural and cultured pearls.  The modifying words are of five main categories:
        1.Geographic localities: Although some geographic modifiers have taken on meanings relating to characteristics of the given pearls, the names per se indicate only where the pearls were recovered and/or marketed.  Examples include African, Arkansas, Australian, Biwa (Lake Biwa, Japan),
Bombay, California, Campeche (Venezuelan gulf), Celebes (Indonesia islands), Ceylon, Egyptian, Elster (Saxony), European, Fiji (Islands), Gambier (a South Pacific Island), Haiti, Indian, Japan(ese), La Paz (Baja California), Madagascar, Madras (India), Manila, Merguian (eastern shore of the Bay of Bengal), Nassau (Bahama Islands), Palau (Caroline Islands), Panama, Passau (Bavaria), Persian Gulf, Philippine, Red Sea, Scotch or Scottish, South Sea, Sulu (archipelago of Phillippines), Tahiti (may include nearby Tuamotu pearls), Thursday Island (in Torres Strait), Tuticorin (India), Venezuela, Yangtze River and Zanzibar.
        2. Name of "parent" mollusc i.e., its scientific family, genus or species (usually not italicized!) or its common name:  Examples include Abalone (marine
gastropods - family Haliotidae, commonly called ear shells) which are typically blister pearls; Biwa mussel (Hyriopsis schlegelii  (von Martens, 1861)), Blue-point (fresh-water mussel Quadrula undulata (Barnes));   Butterfly mussel/clam (Ellipsaria lineolata (Rafinesque, 1820))  Cockscomb mussel (Cristaria plicata (Leach, 1815));  Conch and helmet conch (marine gastropods, Strombus Linaeus, 1758 sp.  & Cassis Scopoli, 1777 sp.);  Hackle back (fresh-water mussel Symphynota/Lasmigona complanata (Barnes, 1823)), sometimes called hatchet back or heel splitter clam;  Margaritifera (fresh-water mussel Margaritifera margaritifera (Linnaeus, 1758));  Meleagrina (Pinctada Roding, 1798 sp.); Mussel;  Mytilus (family Mytilidae);   Niggerhead (fresh-water mussel Quadrula ebena);   Pinctada, a "pearl oyster" genus, especially  Pinctada margaritifera (Linnaeus, 1758) and Pinctada maxima (Jameson, 1901), but also including others, such as  P. maculata (Gould, 1850), P. mazatlanica (Hanley, 1856) and   P. fucata (Gould, 1850) & P. martensi (Dunker, 1872), the last two of which are also called Akoya pearls;  Pinna (Pinna nobilis (Linnaeus, 1758)), which is a "wing shell";   Quahog (salt water clam Venus mercenaria  Linneaus, 1758);  Rainbow-lipped or Pacific wing oyster (Pteria sterna (Gould, 1851));  Sheepnose (fresh-water mussel Plethobasius cyphyus (Rafinesque, 1820)), sometimes referred to as bullhead clam;  Triangle oyster (Hyriopsis cumingii (Lea, 1852));  Unio (fresh-water mussels of this genus);  [and]  Warty-back (fresh-water clam Quadrula pustulosa (I. Lea, 1831)).                           
        3. Color – See Colors under DESCRIPTION and the notes about Colored pearl and Fancy pearl in the following list. 
        4. Shape – Relatively commonly used examples are baroque (irregular spheroidal pearls), button or haystack (dome-shaped pearls with one virtually planar surface
[typically blister pearls]), dog-tooth (roughly tusk-like), drop (ovoid or tear drop-shaped), egg, pear (also termed pear drop or pear eye), turtle-back (pearl with an irregular surface pattern that roughly resembles the elevations and depressions on a turtle's shell [typically blister pearls]) and wing (resembling a wing or part thereof). 
        5. Others –  A) terms once applied but currently
virtually obsolete  and  B) terms, most of which have fairly widely recognized connotations that indicate certain relatively important information about those pearls.  A few of the latter terms are included on the following list. -- Note: In order to avoid repetitious citations to Shipley (1951) on this list, an asterisk (*) precedes each of the terms defined in his "Dictionary of Gems and Gemology," and "definitions" enclosed in quotation marks are directly from his Dictionary. 



D. Pearls.  Names of the pearls and the mollusks within which each kind was formed follow:  Upper left, Akoya cultured pearls --
saltwater akoya-gai oyster (Pinctada martensi (Dunker, 1872));  upper right, South Sea cultured pearls --  silver/white-lipped oysters (Pincada maxima (Jameson, 1901));  lower left, Tahitian cultured pearls -- black-lipped oyster (Pinctada margaritifera (Linaeus, 1758));  lower right, Freshwater cultured pearls -- diverse freshwater clams and mussels. Sizes, not given, are not the same for all photos. (© photos by Shigeru Akamatsu). 


USES:    Necklaces and chokers; earrings and finger rings; and pendants, including those hung as parts of crownsRelatively recently,  some odd-shaped pearls – typically freshwater cultured pearls – have been used to fashion jewelry with attractive patterns – e.g., flower shaped pendants and pins.  And, as already mentioned, multi-colored pearls, though seldom used in necklaces, have found use in flat settings of rings, earrings and small pendants.



E. Pearls.  These pearls were part of the collection of the former Shah of Iran.  The 35mm transparency used for this scan is one of several that David Brittain, former CMU photographer (now deceased), obtained permission from Lou/is Zara (1910-2001) to reproduce from his Mineral Digest for my use;  as is evident, the original was a composite.




F. Pearls. Three strands of diverse cultured pearls. M. Freeman.   photo by Jeffrey A. Scovil)


OCCURRENCES & NOTEWORTHY LOCALITIES: The names of geographic localities listed under OTHER NAMES are an indication of the many places pearls -- natural and/or cultured -- have been recovered.  Types of pearls considered typical of some of these localities are described by Smith and Phillips (1962).  China is a particularly large producer of freshwater pearls of many colors and shapes, some of the spheroids of which have diameters that range up to 15 mm.   Tahiti is a noted source of cultured black pearls, and Mexico's Sea of Cortez is famous for its "baroque cultured pearls with beautiful color." (Kautsky, 2006)

REMARKS:  Different suggestions have been made so far as etymology of the term pearl:  Although it is generally accepted as stemming back via the French perle to the Latin perla, its root(s) are questioned;  professional etymologists have made so many different suggestions it  seems unproductive either to summarize or repeat any particular one here.

Pearls are usually washed in water or hydrogen peroxide and sometimes buffed to increase their luster, but unlike most gemstones, they do not need to be polished or otherwise modified to make them look the way most people want them to.  Indeed, it is widely accepted that any attempt to polish, carve or otherwise fashion a pearl would spoil its appearance.  Nonetheless, several procedures have been applied in attempts to enhance the appearances of pearls: Some pearls have been bleached;  some have been coated -- e.g., with a silicone polymer;  some have been heated;  some have been irradiated;  some have even been faceted -- e.g., the so-called "Komatsu Flower Pearls," which are indeed rather stunning (see Figure 9 in Johnson and Koivula, 1997);  some have been dyed with colors that virtually cover the visual spectrum:  Apparently in the past, "the usual process ... [was] to force dye into the pearl by way of the drill hole." (Shipley, 1951, p. 69). Currently, several means are used with one of the most popular, at least for  cultured pearls being the implanting of dyed nuclei.    One report of dyed pearls is especially interesting to me:  It notes that the "beads had been subjected to such a drastic dying process that they were completely saturated to the center of the mother-of-pearl bead by the unnatural-colored dye. They resembled antique rose petal beads more than pearls.” (Liddicoat, 1964). -- I find Dick's analogy of particular interest because I suspect I may be one of very few now living who rather recently has made rose petal beads and knows what he meant. 

Care of pearls.  One must keep two things in particular in mind:  1)The luster of pearls may be reduced by contact with perspiration, the chlorine use in some swimming pools, and chemicals such as those in some perfumes and hairspray.  2) Pearls are easily scratched by such things as glass sequins and other jewelry.  Considering the fact that no means has been found to restore "damaged" pearls to their original state, one should take great care both while wearing and storing pearls.  Wiping pearls off with a soft cloth (NOT washing them!) each time after they have been worn -- particularly if they have been in contact with one's skin -- is a good habit for those who wear pearls.  In addition, it is of at least passing interest that Dubin (1987) has noted that long-time storage has been recorded as resulting in pearls being reduced to dust;  BUT, this record seems to represent an anomaly because "records of fossil pearls are ... fairly numerous."  (Cox, 1969, p.N78).

As one might suspect, virtually all molluscs secrete material on top of or around foreign particles -- e.g., parasites, sand grains and seaweed -- that become entrapped in their mantles or between their mantles and shells.  When this process involves molluscs with mother-of-pearl shells, the secretion is typically nacreous and the common result is a pearl.  Pearls are produced whether the foreign particles get into the mollusc naturally or are put there by man.  So, as one might expect, a very large percentage of the pearls that are marketed are of the latter type, and they are generally referred to as cultured pearls. -- As noted by Pechenik (2005, p.208): "Natural pearl formation is a fairly rare event ... [so] Humans increase the frequency of pearl production by surgically implanting pieces of shell (usually from freshwater bivalves) or plastic spheres between the shell and mantle of mature oysters, and then keeping the oysters alive for 5 to 7 years.  Note that cultured pearls form in a perfectly normal manner;  humans intervene only in getting the process started."   Methods used to produce cultured pearls and the diverse shapes and compositions of the implanted pieces are described extensively in many publications;  consequently, it seems unnecessary to repeat them here.  It does seem historically noteworthy, however, that Kokichi Mikimoto (1858-1954) is usually credited with discovering the methods for mass-producing cultured pearls that revolutionized the pearl industry, and there is the interesting tidbit that in at least the Baja California setup, "Before being returned to the sea for the ... final cultivation state, each pearl oyster ... was individually protected to discourage natural predators.  Some were encased in wire mesh;  others ... were outfitted with handmade spiked "suits of armor." (see Cariño & Monteforte, 1995, Fig.14).
 
Speaking of history, two additional notes: "Among the earliest surviving examples of pearl jewelry is a three-strand necklace of an Achaemenid princess of about 350 B.C., found at the site of Susa, the ancient royal Persian winter residence." (Dubin, 1987, p.297).   And, so far as North America, "Archaeologist Stuart Struever... describes the discovery near St. Louis of a first century A.D. grave in which a high-ranking member of the Hopewell culture was buried in a log tomb with armlets and necklaces of freshwater pearls...[the arrangement of which] suggests that they had been attached to a garment, now deteriorated." (ibid., p.263).  One "New World" use of pearls  (or use of "New World" pearls -- your choice) that sticks in my mind is the story that had Amerindian Chief Powhatan, Pocahontas' father, wearing a raccoon cloak and long strings of pearls when he was overseeing the pending execution of John Smith that legend has Pocahontas as stopping.

In the description of the foundation stones of the "New Jerusalem," it is written, "The twelve gates were twelve pearls, each of the gates made of a single pearl."  (Revelation, chapter xxi, verse 21; Revised Standard Version of "The Holy Bible").  According to S.H. Ball (1935), the term Maharatnani is a collective term that has been applied from time immemorial by Hindus to what they consider the five great gems -- diamond, pearl, ruby, emerald and sapphire. 

"The pearl farms were one of the first private enterprises allowed by the Chinese government." (Avi Raz per Kautsky, 2006)
 
A few pearls have gained fame in the literature of gemology.  The "Hope pearl," once owned by the owner of the "Hope diamond" is perhaps the most frequently mentioned:  It is described as "nearly cylindrical, ... measures 2 inches (51 mm.) in length and 4½ inches (114 mm.) in circumference about the thicker, and 3 1/4 inches (83 mm.) about the thinner end, and weighs about 3 oz or 1800 pearl-grains (450 carats).  About three-quarters of it is white in colour with a fine orient, and the remainder has a bronze tint." (Smith and Phillips, 1962, p.476-476).
  
I apologize for the fact that I did not include pearls when I was working on concretions and compiled the "Carbonate Concretions Bibliography" that is also on this web site.  I regret my oversight because, among other things, it certainly would have facilitated and expedited my compilation of the information given in this entry(!).  Pearls are, of course, carbonate concretions, albeit biochemically produced by molluscs, and should have been included.
 
One of the "pearls of wisdom" that sticks in my mind from my days in Sunday School is
  "≃Cast not ye, your pearls before swine ..." from Matthew (vii., 6).  But, the first two lines of James Russell Lowell's poem "In a Copy of Omar Khayyam" seem to provide a more appropriate ending for these remarks:  "These pearls of thought in Persian gulfs were bred, / Each softly lucent as a rounded moon." 

Freshwater pearls -- found in fresh water mussels --  are the "State Gemstone" of Kentucky and Tennessee.

SIMULANTS:  As most people dealing with pearls, I do not consider cultured pearls to be simulants -- see the fourth paragraph under REMARKS.  Consequently, the following simulants should be considered to be simulants of pearls, both natural and cultured.  As also previously noted, I believe that anyone who feels the need to distinguish between natural and cultured pearls should contact an expert with access to appropriate instruments.  (Nevertheless, I must admit that I have used some other methods in attempts to make such distinctions.  For example, recalling how we candled eggs in my father's store in Hammond, New York, where he took eggs, among other things, from farmers in trade for goods, I have "candled" pearls and am convinced I was able to detect nuclei in some of them, which, of course, indicated them to be cultured pearls.)

       
Historically,  "Clay spherules, coated with mica powder and baked to create the iridescent effect typical of pearls, were discovered amongst the ancient remains of cremated Indians, while in ancient Rome it was customary to silver-plate glass spherules and then coat them with another film of glass in order to render them lustrous." [and "From the second half of the XX Century, several 'alternative artificial products' were developed, almost always based on mineral salts, and used to coat mother-of-pearl, glass or carbonate spherules. The lead carbonate employed in Japan is a typical example, which has the advantage of being white in color, and of recalling the orient of the pearl. ... [and] Coatings based on bismuth and mica powder are frequently used, as they give the surface a luminous, white appearance. Some plastic iridescent imitation pearls ... are widely used for fashionable bijoux jewelry." (Rolandi, 2004).
        The substance called "essence d'orient," which is made from certain fish scales, is noteworthy:  It has been used as the coating on, for example, glass beads sold as pearls, and some of those imitation pearls do have a luster and orient that closely resembles natural and cultured pearls. A short description of "essence d'orient," its discovery and its production is given as the last paragraph of the REMARKS in the FISH SCALES entry. 
       
Another aspect of this topic also seems noteworthy:  Particularly in the past, necklaces have included both natural and cultured pearls AND a few included imitation pearls along with one or both of them. 

        A few noteworthy examples of pearl simulants follow:
 
Bathed pearls - "Among the most recent imitations are mother of pearl spherules covered with iridescent nylon film, often commercialized under such inaccurate names as “bathed pearls”, or other such imaginative names (angel, sheba, mikomo, takara, Kobe, Nikko, Sumo, Fiji, Aloha), or worse still, 'improved cultured pearls'. The mother of pearl spheres are immersed several times in enamels based on plastic substances, and mixed with lead carbonate, mica and titanium oxide. A drying process is carried out after each immersion, and at the final stage they are polished. Results are improved as the number of immersions is increased." (Rolandi, 2004). - [Close examination suffices.]

Bohemian pearls - "Mother of pearl protuberances, meticulously cut and buffed so well that they seem identical to irregular pearls and are often difficult to identify. They are principally produced and commercialized in Bohemia and Russia." (Rolandi, 2004). - [Cut areas can usually be spotted rather easily with a 10x hand lens.].

"Cat's-eye pearls" - These are pieces of shell that have been sculptured to give them pearl-like shapes.  They also have been "represented as non-nacreous natural pearls." (Hainschwang, 2011)

Coconut pearls - These "pearls" as perceived/proclaimed, seem unlikely to exist;  if they do, they would be biochemical products associated with plant growth.  They have been described as a hoax by professional botanists for several years:  Most so-called "coconut pearls" have come from clams (see Armstrong, 2004). - [Until a "pearl" of such origin is proved to exist, anything suggested here would be superfluous.].

"Coque de perle" - name given nacreous sections, especially the center of the whorl, of nautilus shells fashioned into shapes resembling pearls
. - [Appearance suffices.].

Coral - P
ink conch pearls have been simulated by coral. - [Appearance suffices.]

Elephant pearl (= elephant tusk pearl = ivory pearl = gaja mini = gaja-
muthu)  -  roughly spherical mass, made up of concentric layers of dentine deposited on a "foreign body"  nucleus, formed within an elephant's tusk;  these are most likely to be found in tusks of elephants who have been sick or have damaged tusks (Robert Weisblut, personal communication, 2006). - [Appearance should suffice;  superior hardness is conclusive.].  These, in turn, have been  simulated, apparently because they are revered  by some elements of  Sri  Lankan and Indian groups.  At least some of the simulants have been shown to have been "fashioned from the molar tooth of, most likely, an Asian elephant." (Singbamroong, 2008)

Glass-based pearls - Glass beads are part of several pearl simulants.  The glass may be of just about any composition, including so-called alabaster glass, milky glass and Venetian glass;  the material giving the pearl-like appearance may be inside hollow glass beads or on the outside where it was applied by dipping or spraying. - [Appearance suffices.].

Hematite (var. specularite) - Spherical hematite beads resemble black pearls. - [Hematite has a superior hardness - H. 5-
6½  and higher specific gravity  ~5.25.  See Hematite entry on GEMROCKS site.].
 
Hinge pearls - This is a "trade term for pearl shapes cut from the hinge [of a fresh water mussel?]." (Shipley, 1951). - [Appearance suffices.].

"I pearls" -  "Because of the confusion created by numerous commercial names, the Japan Imitation Pearl & Glass Articles Association has suggested a new nomenclature to describe imitation pearls manufactured in Japan:  the use of  'I Pearl' together with an indication of the base material, such as shell, glass, or plastic.  The letter I stands for 'imitation' and also for the place of production, Izumi City.  'I' (Ai) also means 'love' in Japanese." (Johnson & Koivula, 1997, p.306)  The diverse imitations noted -- all of which are on this list -- follow:  Spherical beads  (e.g., alabaster glass, plastic or shell) coated with either essence d'orient or lead carbonate.  Such pearls are sometimes referred to by such names as "imitation cultured pearls," "man-made pearls" and "shell pearls." (ibid.)

Indestructible pearl - name sometimes given Majorican pearls (q.v.)  "An imitation pearl ...  Fairly durable, but not indestructible." (Shipley, 1951, p.110).

Major(i)can pearls - Two descriptions seem relevant: 1."Majorca Pearls ... [--] Each layer, twenty nine in all, is applied by dipping the base into the hemage, allowing it to dry, polishing it by hand to remove bumps and blemishes, and repeating the process to build up the density and uniformity in color. The exact specific process and composition of the hemage is a closely guarded secret known only to the producers on the Isle of Majorca, Spain. Majorca Pearls are considered to be the finest simulated pearls made."(Jewelex, nd).  [and]  2."A new process of coating rather than lining the opalescent glass spheres with Orient essence ... To obtain an interferential effect similar to that of the natural orient, imitation pearls have to be immersed firstly in a bath of clear cellulose acetate, and subsequently in a bath of cellulose nitrate, so that they harden. As a result, the surface becomes velvety and iridescent, very similar in appearance to that of natural and cultured pearls." (Rolandi, 2004, who also notes that similar imitations have plastic or porcelain cores.) - [If the core material is exposed, appearance suffices.].

Mother-of-pearl pearls - Two variants are relatively common:  1) pearl shapes cut from mother-of-pearl molluscs; and 2) crushed nacreous shells that have been sintered into spheres and other pearl shapes. - [Appearances suffice.].

Parisian pearls (= Paris pearls and French pearls)  - glass-blown spheres, the insides of which are coated with essence d'orient and filled with wax. - [Texture differs from that of most pearls -- see Miscellaneous under DESCRIPTION]

Plastic Pearls - name sometimes given to simulants that are plastic beads to which the pearl-like appearance has been applied by dipping, painting or spraying. -[These simulants have an inferior Specific Gravity, and the coating of most of them is rather thin and tends to peal off rather easily.].

Richelieu pearl - "a brand of imitation pearl" (Shipley, 1951, p.194). - [This is included here as an example of several trade name pearls for which I have found no description.]

Roman pearls - "“Roman pearls” are composed of an alabaster core bathed in various different iridescent substances (isinglass, lustrous oyster scales, mother of pearl powder)."
(Rolandi, 2004). - [Appearance suffices.].

Shell -  Beads fashioned from nacreous portions of mollusc shells
, and in some cases dyed, have been misrepresented as pearls, including the so-called Melo "pearls." - [Close examination suffices because these beads are laminated.].
 
Shell pearls -
This name is sometimes given to simulants that consist of spheroidal shell cores that have been given pearl-like appearances as the result of dipping, painting or spraying them with some pearl-appearing material. - [The coating of most of these simulants is relatively thin and tends to peal off rather easily.].

Tecla pearls - "trade-marked name for both solid and wax-filled imitation pearl beads"  (Shipley, 1951, p.228). - [In general the specific gravities of these simulants are as follows: Hollow glass (including wax-filled) beads - <1.55;  solid glass - typically 2.85-3.18, with those >3.0 most common, and a few as low as 2.53.].

Wax-filled pearl simulants (= some imitations described as Hollow and also some that have been given names such as
"Bourguignon pearls" and "Venetian pearls") - Each of these "Imitation pearl[s is] made of a hollow glass sphere coated with essence d’orient and filled with wax." (Shipley, 1951);  slightly different processes are involved in forming some of these simulants -- e.g., "Venetian pearls" have the essence ... added while the glass is being fused. - [inferior specific gravity -- typically <1.55].

REPLICAS:  This is a case where the simulants may be considered replicas.  Also, so far as the mollusks that produce pearls, their replicas are noted under this heading in the SHELL... entry.

==================++++&&&++++====================


ADDENDUM.  Some Specific Gravity values recorded for pearls.


  
               
 Localities  Smith &  Phillips, 1962
     (from Figure 138)

       Webster, 1975
     (from Table 21.1)
      Ranges

   
  Specific gravity
Specific gravity  Remarks        
  Persian Gulf                  
  2.66-2.75   2.68-2.74   
creamy-white*       2.66-2.75  
  Gulf of Mannar  
  2.68-2.74 
pale creamy-white*
        


Australia
 
 2.66-2.78



--
\
\

Australia, north coast
 
  2.68-2.78
silver-white*     } 2.66-2.78   

Australia, north-west coast


  2.67-2.78
silver-white*
--//

Venezuela
  2.65-2.77
  2.65-2.75
white*
      2.65-2.77

Japan
<2.65-2.76   2.66-2.76
white, greenish tinge*
    <2.65-2.76

Florida & Gulf of California
  2.85 (pink conch, ?locality
  2.85
pink, etc.**
      2.85

Gulf of California   2.61-2.69 (no local given)
  2.61-2.69
black
      2.61-2.69







Freshwater pearls:



    <2.65->2.78

North America & Europe
<2.65 - 2.76 (No.Amer.)
  2.66->2.78
white#
     





     

Cultured pearls:



      2.705->2.80

No locality given
 2.705 - >2.80



Japan

  2.72-2.78
white*


   Non-nucleated



      2.67-~2.70

Japan

  2.67-2.70
white+


Australia
~2.70
white*


                * Mollusc host a species of Pinctada genus.
              ** Mollusc hosts: Great/queen conch (Strombus gigas Linnaeus, 1758) for pink pearls;  abalone (family, Haliotidae) for
                           others, which are indicated as greens, yellows, blues, etc.
                # Mollusc hosts indicated to be species of Unio genus.
                + Mollusc host indicated to be Hyriopsis schlegeli (Martens, 1861).

It also seems noteworthy here that especially in the past, specific gravity (density) was used as a criterion to distinguish many pearl simulants from natural and cultured pearls.  For example, "pearls" -- i.e., pearl simulants -- with hollow glass beads as a component have specific gravities (e.g., ~1.55) that are markedly lower than those of real pearls and most "pearls" that consist of solid glass beads coated with "essence d'orient" have specific gravities (e.g., > 2.85) that are higher than the specific gravities of virtually all natural and cultured pearls (Webster, 1975, p. 497). 

      
                                                                          ==================++++&&&++++====================

NOTE:  As of this date -- September 20, 2007,  although a few changes and additions, which will be in red type, may be made in the future, for the most part, this entry will no longer updated like the other entries in this file.  My recommendation for anyone who wants to keep up-to-date so far as what is recorded in the literature about pearls -- natural, cultured, ... -- is that (s)he should periodically review pertinent articles etc. publlished in Gems & Gemology.   Articles with especially noteworthy information will be listed in the References Cited and be listed here: 
                  McClure, Kane and Sturman (2010) include explanations relating to treatments that have given some of the so-to-speak exotic colored pearls. 

   
                                                                                                                                                                           RVD



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