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MOP
MOP is an abbreviation for “Mother Of Pearl”. It is technically the Nacre found in Sea Shells.
Nacre pronounced /ˈneɪkər/[1] or "NAY-kər", also known as mother of pearl, is an organic-inorganic composite material produced by some mollusks as an inner shell layer; it is also what makes up pearls. It is very strong, resilient, and iridescent.
Nacre is found in some ancient lineages of bivalve gastropod and cephalopod. The inner layer in the great majority of mollusk shells is porcellaneous, not nacreous, frequently resulting in a non-iridescent shine or less commonly in non-nacreous iridescence such as flame structure (e.g. conch pearl).
Pearls and the inside layer of pearl oyster and freshwater pearl mussel shells are made of nacre. Many other families of mollusk also have a nacreous inner shell layer, including marine gastropods such as the Haliotidae, the Trochidae and the Turbinidae.
Appearance
Nacre appears iridescent because the thickness of the aragonite platelets is close to the wavelength of visible light. This results in constructive and destructive interference of different wavelengths of light, resulting in different colors of light being reflected at different viewing angles.
Structure
Nacre is composed of hexagonal platelets of aragonite (a form of calcium carbonate) 10-20 µm wide and 0.5 µm thick, arranged in a continuous parallel lamina.[citation needed] These layers are separated by sheets of organic matrix composed of elastic biopolymers (such as chitin, lustrin and silk-like proteins). This mixture of brittle platelets and the thin layers of elastic biopolymers makes the material strong and resilient, with a Young's modulus of 70 GPa. Strength and resilience are also likely to be due to adhesion by the "brickwork" arrangement of the platelets, which inhibits transverse crack propagation. This design at multiple length sizes increases its toughness enormously, making it almost equivalent to that of silicon.
The crystallographic c-axis points perpendicular to the shell wall, but the direction of the other axes varies between groups. In bivalves and cephalopods, the b-axis points in the direction of shell growth, whereas in the monoplacophora it is the a-axis that is this way inclined.
Formation
Nacre formation is mediated by the organic matrix, which controls the onset, duration and form of crystal growth. Individual aragonite "bricks" quickly grow to the full height of the nacreous layer, and expand until they abut adjacent bricks. Bricks nucleate on randomly-dispersed elements within the organic layer. This produces the hexagonal close-packing characteristic of nacre. Nacre differs from fibrous aragonite – a brittle mineral of the same form – in that the growth in the c-axis (i.e. perpendicular to the shell, in nacre) is slow in nacre, and fast in fibrous aragonite.
Function
Nacre is secreted by the epithelial cells of the mantle tissue of various molluscs. The nacre is continuously deposited onto the inner surface of the shell, the iridescent nacreous layer, commonly known as mother of pearl. The layers of nacre smooth the shell surface and help defend the soft tissues against parasites and damaging debris by entombing them in successive layers of nacre, forming either a blister pearl attached to the interior of the shell, or a free pearl within the mantle tissues. The process is called encystation and it continues as long as the mollusk lives.
Evolution
The form of nacre varies from group to group. In bivalves, the nacre layer is formed of single crystals in a hexagonal close packing. In gastropods, crystals are twinned, and in cephalopods, they are pseudohexagonal monocrystals, which are often twinned.
Following are different types of Sea Shell whose Nacre is used by us to create MOP work. They are mostly trade names and not biological names of sea shell. Click on the photos to enlarge them.
The most famous MOP Shells of the world. Their names, origion and notes:
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SILVER-LIP OCEAN PEARL OYSTER (Pinctada maxima), Australia: a formerly very large shell, used for pistol grips, clothing buttons, fans, and vanity items, which produces the classic white M.O.P., referred to in France as "poulette" or "nacre blanche". Shell sizes have greatly diminished in recent years, due to a decline in diving for "wild caught" shells, making it increasingly difficult to get larger pieces. |
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GOLD-LIP OCEAN PEARL OYSTER (Pinctada maxima), Indonesia and the Philippines: the source of our GOLD M.O.P., which comes from a thin yellow layer underlying the white nacre. White material from these shells typically has lots of colorful iridescent "flash". |
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WING SHELL (Pteria penguin), Philippines, Tonga: large, thin-shelled, and scoop-shaped, yields the beautiful pinkish-brown and highly iridescent BROWN M.O.P. |
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BLACK-LIP OCEAN PEARL OYSTER (Pinctada margaritifera), Tahiti: this shell produces the famous and exotic black jewelry pearls, but has become very hard to get in sizes large enough to make inlay materials from, so availability is sporadic at best. The French term is "nacre grise". |
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CAPIZ (alt.: KAPIS), or WINDOW SHELL (Placuna placenta), Philippines: round, small (2"-3"), and flat, has been used for centuries in native handicrafts and for making lampshades and primitive transparent windows. It is one of the very few shells that can be softened enough by boiling that it can be cut with scissors (making it popular in craft shops), but it is also very fragile and flaky which limits it's uses in modern inlay work. |
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PEN SHELL (Pinna rudis), Indonesia: traditionally used for making small beads, sheets made from this large, thin shell are not pearlescent but do have a faint and silky chatoyance. Color is mottled light tans to dark purplish-browns, somewhat similar to tortoiseshell. |
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AGOYA (also AKOYA) OYSTER (Pinctada fucata, also listed as P. martensii), Japan: this is the small shell which is used to produce cultured pearls. Closely related to the larger ocean pearl oysters, but has a slightly "bumpier"-looking internal figure and a pale straw-yellow color that shows wonderful pink and green flashy highlights. |
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DONKEY EAR ABALONE (Haliotis asinina), Philippines: a tiny little thin-shelled animal, often used whole for earrings and pendants, its long narrow shape looks like a donkey's ear. Palest pink with no black lines, but plenty of very fine striated texturing to give it interest, and some iridescence. Not thick enough to get solid blanks from. |
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GREEN SEA SNAIL (Turbo marmoratus), from Okinawa, Japan: widely popular in the 1800's and early 1900's for jewelry, fans, buttons, small box ornament, and instrument inlay. After supplies from Okinawa diminished new sources were discoved in Africa, but the main fishing grounds in Africa were worked out trying to keep up with the Japanese market, so has not been available from that area for many years. Beautiful, clear, creamy iridescence, and has a rolling light to it imparted by the strong curvature of the raw shell structure. Traditionally known in France as "burgo", "burgau", or "burgaudine". |
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GREEN TURBO SHELL (Clorostoma xanthostigma), Africa: a small cone-shaped snail, producing the most brilliant iridescence of any variety of pale-colored shell (but, see Korean Awabi). Expensive, but breathtakingly beautiful coloration. |
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KOREAN AWABI ABALONE (Haliotis supertexta), S. Korea: a small, pale-colored abalone, which has a fine internal wrinkly/bumpy/wavy figure but possesses almost the same intensity of color and iridescence as Turbo shell! Discover the joys of working with "pale" and pastel shells! |
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JAPANESE AWABI ABALONE (Haliotis madaka, formerly gigantea), Japan: until the beds were overfished, this was one of the largest abalone species, second only to the Red abalone. The nacre is very pale, but with strong "washboard" figure, though not as tightly rippled as the best Green abalone can produce. Seen often as a backing veneer in antique fans, known in France as "nacre d'orient" and in England as "goldfish". The shells are too thin to make thicker solid blanks, but see GRAVLAM. |
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ORMER (alt.: French "ORMEAUX"), or SEA EAR (Haliotis tuberculata), English Channel: small, thin, pale-colored abalones traditionally used in the frogs of English violin bows. |
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RED ABALONE (Haliotis rufescens), northern California: the biggest abalone in the world, its name refers to the red "bark" covering the outside of the shell. Nacre is pale pink to intense dusky pinks, greens, and violets; the central muscle-scar area of the shell yields the much sought-after dark and burly "heart" pieces. Because of overfishing, otter depradation, and a recent outbreak of mysterious "withering foot disease", the commercial fishery has been shut down indefinitely, so availability is zero at present. |
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GREEN ABALONE (Haliotis fulgens), southern California and Baja, Mexico: a beautifully colored shell second only to Paua abalone, but due to severe overfishing not many of the color-producing larger shells are available, so material tends to be much paler than in the past. "Heart" is very densely colored and figured, with deep greens, blues, and pinks, but small shells yield very little of this, so availability is always limited. |
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PINK ABALONE (Haliotis corrugata), southern California and Baja, Mexico: a well colored shell, pale to predominantly darker pinks. Underused, as it is difficult to process because of a crumbly consistency, but finished products work fine, and it is becoming a popular substitute for the increasingly hard-to-find Green abalone. |
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PAUA ABALONE (Haliotis iris), New Zealand and neighboring islands: indisputably the most colorful nacreous shell in the world, typically deep blue or green, but even the pink material turns bluish when viewed at an angle! A smallish shell with lots of other life forms eating holes in it, but since the fishery has been tightly managed for many years, good quality shell is available. If you see Paua jewelry for sale, it has probably been dyed to intensify the color and may even be dyed Green ab. (none of our shell is dyed or "enhanced" in any way). |
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VIOLET OYSTER (Mytilus edulis), the edible “common” or “blue mussel” found widely from Southern France and the British Isles to the Atlantic coast of Canada and the Northern U.S.: This in also found in Asia. The Asian variety we process runs a deep violet color, almost black if not in strong light, many pieces with a fine “ripple” figure. Because these shells are only 3”-4” long, very thin, and dished, the blanks produced are also very small and it's hard to get thicknesses over .030” (.76mm). Exotic, and worth the effort! |
Following are the different types of inlays which are formed by different Shell whose Nacre is used by us to create MOP work. Click on the photos to enlarge them.
Here is an example of small panels made of different patterns and designs of MOP. Also we can see MOP overlay done on vase and decorative urns.
 
Here are two examples of MOP inlay work. One is a floor tile and other is Abalone overlay on a marble pillar. There is a glass carved out of solid block of marble which is overlayed by Abalone. Click on the photos to enlarge them.
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