WO2015104509A1

WO2015104509A1 - Method for marking nacre

Info

Publication number: WO2015104509A1
Application number: PCT/FR2015/050047
Authority: WO
Inventors: Olivier Tillement; Gérard PANCZER; Thomas BRICHART; Matteo Martini; Alain CAUSSINUS
Original assignee: Universite Claude Bernard Lyon I; Centre National De La Recherche Scientifique - Cnrs; Monaco Gem Lab
Priority date: 2014-01-10
Filing date: 2015-01-09
Publication date: 2015-07-16
Also published as: FR3016440A1; FR3016440B1

Abstract

The invention pertains to the field of jewellery, especially nacreous pearls used in jewellery. Said invention especially relates to the development of a method for marking and/or labelling cultured pearls. The invention more generally relates to a method for marking a solid comprising at least a nacre coating, said method comprising the immersion of said solid in an aqueous solution comprising a tracer which is photoluminescent in the presence of said solid for a sufficient amount of time to allow the fluorescent tracer to adhere to the nacre coating.

Description

PROCESS FOR MARKING NACRE

The field of this invention is that of jewelery, and in particular pearl beads used in jewelry. This invention relates in particular to the development of a method for marking and / or labeling the cultured pearls. The invention more generally relates to a method for marking a solid comprising at least one mother-of-pearl coating, said method comprising immersing said solid in an aqueous solution comprising a photoluminescent tracer in the presence of said solid, for a time sufficient to obtain the attaching said fluorescent tracer to the mother-of-pearl coating.

BACKGROUND TECHNOLOGY

Pearls used in jewelery are organo-carbonated biogenic concretions secreted by the mantle of molluscs. Pearlescent pearls are produced by bivalve molluscs either in freshwater or in seawater. There are 1) fine pearls - very rare on the market - formed without any human intervention, and 2) cultured pearls produced by grafting. outer mantle epithelium fragment with or without nucleus implantation. The production of cultured pearls concerns

mainly white pearls from the South Seas (Australia, Indonesia, Philippines, Burma) for 35, freshwater pearls (China) for 24, Akoya pearls (Japan, China) for 22% and Tahitian pearls ( French Polynesia) for 19% [C.

Tisdell and B. Poirine, Working Paper No. 143 Economics of Pearl Oyster Culture, in The Pearl Oyster: Biology and Culture, Elsevier, P. Southgate and J. Lucas (Editors) (2008) 544 pp.]. This market represents an annual amount of 125 million US dollars.

For cultured pearls with nucleus, after at least two years of culture, the thickness of mother-of-pearl produced around the nucleus is sufficient to allow harvesting. This thickness of mother-of-pearl is most often greater than 0.4 mm and for Tahitian pearls always greater than 0.8 mm (X-ray inspection). The pearls can therefore be marketed.

However, many mostly undeclared treatments are performed especially on freshwater pearls: mineral dyes (eg silver nitrate AgNO ₃ makes pearls black or gray) or organic, X-ray or gamma irradiation (makes black or gray pearls), heat treatments (so-called golden pearls) or bleaching. In addition, mechanical treatments are practiced to increase the luster by reducing surface irregularities or even to improve sphericity. The marking and labeling of pearls are therefore highly sought after channels to ensure the confidence of customers as to the origin and lack of treatment of this natural luxury product. The pearl jewelry market is estimated at $ 5 billion (10% of the global jewelery market), and there is strong competition between the various producing countries (Japan, Australia, French Polynesia, China) and finally, that processes of fitness, coloring, bleaching or even imitation develop, it is of extreme economic and strategic interest 1) to be able to control and guarantee the geographical origin, 2) to control and guarantee a quality based on commercial criteria (color, orient, luster, shapes, dimensions) and 3) to avoid any quality fraud, counterfeiting or treatment (artificial coloring by chemical agents, polishing ...).

Among the marking processes in progress or envisaged, laser engraving [EP 0749799 A2 (1996)], or deposition of gas phase material [EP 0 897 021 A] and the marking are found in the state of the art. of the nucleus before grafting [WO 2005015986

A2]. Pearl pearls are fragile objects, luxury and whose external appearance is the main criterion of quality, actions on the surface such as laser engraving are difficult, and requires more individual marking delicate, long and expensive. It is also necessary not to modify the external optical appearance (orient and color) criterion on which is based partly the value of a pearl. As for the labeling of the nucleus before grafting (either by a marker opaque to X-rays, or by another chemical marker), although infalsifiable and permanent since under the nacrière layer, this process also involves a long, complex and expensive individual marking. In addition, it is necessary to mark a large number of nuclei whose implanted pearls are not guaranteed to present the final quality criteria required, it involves introducing a chemical agent (eg metallic paint) in pearl oyster in contact with seawater, and finally it does not allow to highlight a possible subsequent treatment of the final pearl altering its color or shape.

TECHNICAL PROBLEM AND OBJECTIVES TO BE REACHED

In this context, the present invention aims to satisfy at least one of the following objectives:

- propose a new method of marking pearls, which is simple to implement and economical;

- to propose a method of marking which does not alter the appearance and the quality of the pearls and which is persistent in time; to overcome the drawbacks of the marking methods of the prior art, in particular which allow marking on the finished product;

to propose a marking method that can be implemented on a multitude of beads simultaneously;

- propose a marking method that allows coding information;

to propose a marking which makes it possible to highlight any subsequent treatments modifying its color or its shape,

- Offer marked beads, identifying their quality and / or their geographical origin (tracing) and means of reading the marking of these beads, easy to implement.

BRIEF DESCRIPTION OF THE INVENTION

These objectives, among others, are achieved by the invention, which concerns first and foremost a method for marking a solid comprising at least one mother-of-pearl coating, said process comprising immersing said solid in an aqueous solution comprising a tracer. photoluminescent in the presence of said solid, for a time sufficient to obtain the fixing of said photoluminescent tracer to the mother-of-pearl coating. In a preferred embodiment, said solid is a pearly pearl, for example a pearl of culture, preferably produced by a pearl oyster, for example of the species Pinctada margaritifera.

In a specific embodiment, a plurality of solids are immersed simultaneously in the same bath of said aqueous solution, for example at least one hundred cultured pearls.

Said tracer is preferably incorporated on the surface layer of the pearlescent coating to a thickness not exceeding 20 μιη, preferably at most 10 μιη.

In a preferred embodiment, said photoluminescent tracer is chosen from those detectable by time resolved fluorescence in the presence of mother-of-pearl. Typically, it may be a rare earth ion, for example, a lanthanide. Among the lanthanides, said tracer may be chosen from Gd, Dy, Lu, Yb, Sm, Ho, Eu, Tb, Nd, Er, or mixtures thereof, for example a combination of Gd and Eu. In a particular embodiment, said aqueous solution comprises a combination of at least two photoluminescent tracers, which may be present in the same concentration or in different concentrations. The invention relates naturally to the solid comprising a nacre coating marked according to the marking method of the invention. Thus, the invention relates in particular to a pearlescent pearl comprising at least one tracer or a combination of photoluminescent tracers on the surface layer of the nacrière layer, for example to a thickness of at most 20 μιη of said surface layer, preferably at most 10 μιη, said photoluminescent tracer being detectable vis-à-vis the natural photoluminescence said pearl pearl.

Said pearlescent pearl according to the invention comprises in particular a photoluminescent tracer which may be chosen from a rare earth ion, preferably a lanthanide, for example gadolinium, europium or their mixtures.

The invention also relates to a method for identifying a labeled solid according to the invention or a pearlescent pearl according to the invention, characterized in that it comprises the time-resolved fluorescence detection of the photoluminescent tracer (s). .

In a preferred embodiment, the identification method according to the invention is characterized in that it further comprises the detection of the absolute or relative amounts of a combination of photoluminescent tracers. Another aspect of the invention relates to the detection means suitable for implementing the identification method as defined above.

These detection means may comprise, for example, a time resolved fluorescence detector and signal analysis means in order to identify the presence of the photoluminescent tracer (s) in the labeled solid or pearl pearl.

The invention also relates to the use of detection means above, for tracing and / or identification of the origin of production and / or the quality of a pearly pearl. DETAILED DESCRIPTION OF THE INVENTION

P.4.4.4.4. of. marking of a solid comprising. at least one mother-of-pearl coating The marking method according to the invention judiciously uses the particular structure of the mother-of-pearl, an organomineral hybrid matrix to fix photoluminescent elements thereupon detectable by appropriate means.

Thus, in a first aspect the invention relates to a method of marking a solid comprising at least one mother-of-pearl coating, said process comprising immersing said solid in an aqueous solution comprising a photoluminescent tracer in the presence of said solid, during a sufficient time to obtain the fixation of said photoluminescent tracer within the mother-of-pearl coating. The solid comprising a rey of. nacre

The marking process is applicable to any solid as it has an outer layer or a coating of nacre. Mother-of-pearl is the lining of some mollusc shells, composed of crystals of aragonite and conchyoline, with iridescent reflections. It is a product used for decoration, marquetry, making jewels or buttons. The mother-of-pearl is formed more precisely by the regular superposition of layers of conchyoline, aragonite crystals as well as traces of water and various ions whose particular disposition causes an interference of the luminous radiations giving it its iridescent aspect. Organic substance, the conchyoline is present in very small quantity in mother-of-pearl (about 4 to 6%) and determine its structuring by serving as "cement" with the crystals of aragonite (which represent 90% of the nacre). The mother-of-pearl thus consists of stacked small crystals of aragonite 500 nm thick, separated by a very thin layer (approximately 50 nm) of protein which ensures the toughness of the whole.

The mother-of-pearl layer or coating on the solid to be marked according to the process of the invention is preferably of a thickness of at least 20 μιη, or even at least 100 μιη, for example at least 500 μιη. The solid is preferably spherical, with an average diameter preferably of between 1 and 20 mm, in general between 2 and 12 mm. A more particularly preferred application of the marking method according to the invention concerns the marking of pearlescent pearls. The marking process is suitable for all types of pearls, whether natural pearls or cultured pearls. In a specific embodiment, the labeling process is carried out on a pearl of culture, produced by a pearl oyster, for example of the species Pinctada margaritifera, and in particular the oyster Pinctada margaritifera var. Cumingui who lives in French Polynesia and who allows the production of Tahitian pearls.

The method is simple to implement: it consists in immersing the solid comprising the mother-of-pearl coating in an aqueous solution comprising at least one photoluminescent tracer, for a time sufficient to obtain the attachment of said photoluminescent tracer to the mother-of-pearl coating.

By "fixation" is meant a fixation of the tracer to the solid stable over time. In a preferred mode, applicable to pearlescent pearls, the fixing of the photoluminescent tracer is particularly resistant to different types of washes and / or pearlescent pearl treatments (as described in examples), such as gentle washing with bleach, soap, sweat, water and alcohol. The association can also resist the natural friction of the skin or the textile. On the other hand, preferably, the fixing of the tracer is not resistant to polishing by mechanical abrasion, affecting the surface layer of the pearly pearl.

One of the advantages of the process according to the invention is that it makes it possible to simultaneously mark a large number of solids, for example a large number of pearlescent pearls. To do this, a plurality of solids, for example at least 100 pearlescent pearls, or several hundred pearlescent pearls are immersed in a bath of a solution containing the photoluminescent tracer (s) used (s). ) for their marking.

Preferably, the conditions for bringing the photoluminescent tracer into contact with the mother-of-pearl are such that said tracer is fixed on the surface layer of the pearlescent coating to a thickness not exceeding 20 μιη, preferably at most 10 μιη. In other words, said tracer remains on the surface layer of the pearlescent coating. When applied to the marking of the beads, the marking then does not resist mechanical abrasion (polishing) of the pearl, which generally eliminates a surface layer of at least 10 μιη, and the marking process thus makes it possible to guarantee that the pearls do not not polished.

The choice of the photoluminescent tracer is free, but guided on the one hand by the adsorption or penetration properties for its attachment to the nacre coating and on the other hand by its photoluminescence properties for its detection.

By "photoluminescent tracer" is meant any element, small molecule, macromolecule, metal or organometallic complex, or composition, for emitting a photoluminescent signal alone, or in combination with a natural constituent of the nacre. The photoluminescent signal emitted by the tracer after attachment to the surface layer of the mother-of-pearl must be detectable with respect to the natural photoluminescent signal possibly emitted by the nacre of the said solid, for example, the pearl. By "detectable", it is intended to be able to identify their presence or not in the solid (for example the pearl) beyond a certain concentration and even if possible to quantify their concentration as soon as they are present in the medium.

For the purposes of the invention, the "photoluminescent tracer" has the property of absorbing light energy (excitation light) and of slowly returning it in the form of fluorescent or phosphorescent light (emission light) within a certain time period. preferably greater than 100 ns, and preferably greater than 1 μ8.

Among the photoluminescent tracers that may be used, it is possible to choose, for example, those detectable by time-resolved fluorescence in the presence of mother-of-pearl. These photoluminescent tracers may be chosen from rare earth semiconductors, oxides, fluorides or vanadates, organic photoluminescent molecules (for example tetracycline or calcein), transition metal ions or rare earth ions. linked or not to complexing molecules and / or molecules to improve their absorption and their mixtures and / or alloys.

Typically, these may be rare earth ions, for example, lanthanides.

In a specific embodiment, said photoluminescent tracer is a lanthanide selected from Gd, Dy, Lu, Yb, Sm, Ho, Eu, Tb, Nd, Er, or mixtures thereof, for example a combination of gadolinium and europium. The marking solution

For the implementation of the labeling method, one or more photoluminescent tracers are immersed in a marking solution. The labeling solution comprises at least one photoluminescent tracer, or a combination of at least two photoluminescent tracers, with identical or different concentrations.

The product thus labeled, for example, the pearl thus marked, will emit a specific signal, depending on the type of photoluminescent tracer used, its concentration in the aqueous solution, and the immersion time in the aqueous solution. This specific signature can be used for example to code certain information related to the pearl, including its quality and / or its geographical origin.

The pH of the solution is adapted to promote the marking and to avoid degradation of the product to be marked, for example pearlescent pearls. In a particular embodiment, especially in the presence of lanthanides, a pH of between 5 and 6 will be chosen.

In a specific embodiment, said labeling solution comprises a combination of distinct lanthanides.

The metals of the lanthanide series include atomic number elements from 57 (lanthanum) to 71 (lutetium). For example, in a preferred embodiment, a photoluminescent tracer for the labeling method according to the invention, a lanthanide selected from Gd, Dy, Lu, Yb, Sm, Ho, Eu, Tb, Nd, Er will be used. , or mixtures thereof, for example at least Gd and Eu.

In another specific embodiment, said labeling solution comprises the following photoluminescent tracers: Gd ³⁺ / Eu ²⁺ , Gd ³⁺ / Eu ³⁺ , Mn ²⁺ / Eu ³⁺ , Mn ²⁺ / Pb ²⁺ , Sm ²⁺ / Fe ³⁺ .

In a more particular embodiment, said labeling solution comprises a combination of lanthanides chosen from: Gd, Dy, Sm, Eu, Tb, Nd, Er, for example a combination of Tb and Eu. The concentrations of these lanthanides are example between 10 ^" 5 and 10 ^" 2 M in said marking solution. The lanthanides can be associated with complexing or chelating molecules either naturally present in the nacre or added to the marking solution.

By "complexing molecules" or "chelating agent" is meant any molecule capable of forming with a metal agent, a complex comprising at least two coordination bonds.

In a preferred embodiment, a complexing agent having a coordination of at least 6, for example at least 8, and a dissociation constant of the complex, pKd, greater than 10 and preferably greater than 15, with a lanthanide, will be chosen. .

For the purposes of the invention, dissociation constant pKd is understood to mean the measurement of the equilibrium between the ions in the complexed state by the ligands and those free dissociated in the solvent. Precisely, it is less the logarithm in the base of the dissociation product (- log (Kd)), defined as the equilibrium constant of the reaction which translates the transition from the complexed state to the ionic state.

Such complexing agents are preferably polydentate chelating molecules chosen from families of polyamine-type polycarboxylic acid molecules and having a high potential number of coordination sites, preferably greater than 6, such as certain macrocycles.

In a more preferred embodiment, DOTA or 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid, of the following formula, will be selected:

or one of its derivatives, in particular comprising an aromatic ring. When the labeling is carried out with a mixture of photoluminescent tracers, each type of photoluminescent tracer is preferably characterized by the emission of one or more specific photoluminescence signals, by example of different transmission and / or excitation wavelengths. Examples of implementation of the marking method are described below, without being limiting. So marked such ^

The products obtained after implementation of the labeling process according to the invention are characterized by the presence of photoluminescent tracers of unnatural origin, fixed on their mother-of-pearl coating. The invention therefore relates to such products and in particular, pearlescent pearls, marked by means of the labeling method described above.

The invention thus relates to a pearlescent pearl, for example a pearl of culture, comprising at least one tracer or a combination of photoluminescent tracers on the surface layer of the nacrière layer, for example to a thickness of at most 20 μιη of said superficial layer, preferably at most 10 μιη, said photoluminescent tracer being detectable vis-à-vis the natural photoluminescence said pearl pearl.

Said pearl according to the invention comprises in particular a photoluminescent tracer which may be chosen from a rare earth ion, preferably a lanthanide, for example gadolinium, europium or their mixtures.

The presence of the photoluminescent tracer is in principle uniform on the layer

superficial pearl shell. Preferably, it can be easily removed by polishing.

In a preferred embodiment, the bead comprises less than 1 ppm of photoluminescent tracer. Procédé..4. [identification of a product. The invention also relates to a method for identifying a labeled solid according to the labeling method of the invention or a labeled pearl, characterized in that it comprises the time-resolved fluorescence detection of the photoluminescent tracers. The detection method must make it possible to identify the specific photoluminescent signal of the tracer (s) used for the marking. The method can detect the presence of a combination of photoluminescent tracers present on the labeled solid and / or pearl, and if appropriate, their absolute or relative amounts.

The method includes

a) emitting a light pulsed on the marked solid, for example the pearl, (preferably in the UV) for example with a frequency lower than 1 kHz, b) detecting the light emitted by the labeled solid, for example the pearl, after at least 100 nanoseconds, preferably after at least 1 microsecond after the end of the excitation pulse,

c) sorting the wavelengths or selecting the expected wavelengths according to the photoluminescent tracer or tracers that can be fixed on the solid,

d) detecting the specific light of the photoluminescent tracer (s) capable of being fixed on the solid

e) optionally, also measuring the intensity of the signal to deduce the absolute or relative concentration of each tracer in the labeled solid, for example, the pearl.

The invention is based on the use of photoluminescent tracers capable of emitting (alone or in combination with other elements) a signal after at least 100 ns, preferably at least 1 μ8 after the end of the excitation pulse. The collection of light after at least 100 ns, preferably at least 1 μ8 after the end of the excitation pulse, thus makes it possible to discriminate between the light naturally emitted by mother-of-pearl and the photoluminescent tracers attached to the superficial layer of mother-of-pearl. .

The invention therefore also relates to a device comprising the appropriate detection means for implementing the identification method of the labeled solid, or a bead according to the invention. This device comprises for example

a transmitting device making it possible to send pulsed light onto the marked solid, for example the pearl, (preferably in the UV) for example with a frequency lower than 1 kHz,

a receiver device for detecting the light emitted by the marked solid, for example the pearl, a receptacle or support for positioning the marked solid, for example a bead, said solid being preferably positioned at an angle less than 90 ° between the excitation source, the solid and the detector,

a wavelength sorting or selection device for identifying the emitted light of interest (for example by filters, by monochromator (Czerny-Turner or other type) or by network),

- if necessary an interface indicating the result of the detection, for example,

"Positive" or "negative". Such a device is preferably portable and / or ergonomic, so for example to be used by a non-specialist, for example a customs officer or a jeweler.

The identification method and the devices according to the invention can advantageously be used to identify, for example, the origin of production and / or the quality of a product marked by the marking process of the invention, for example a pearl. pearly.

By way of example, the invention could be implemented to certify the geographical origin and / or the quality of the cultured pearls, for example French Polynesia cultured pearls. A specific combination of photoluminescent tracers is used to encode the geographical origin and / or quality of the pearly pearl. The invention thus provides both the marking method for tracing and / or the identification of the production origin and / or the quality of the pearly pearl, and also the device for verifying / certifying the origin. and / or the quality of a pearl by identifying the presence of specific tracers.

Other applications could be envisaged and the examples below are not limiting.

EXAMPLES.

Description of figures

Figure 1 shows beads immersed simultaneously in the marking solution for the required time

Figure 2 shows the rinsing phase of the marked beads Figure 3 shows the sample holder for laboratory detection of the individual marking of a pearl

EXAMPLE 1 Method for labeling cultured pearls with Mn 2+ manganese ions A concentrated labeling solution of manganese ions is prepared so as to obtain a concentration of 50 g / l of MgCl ₂ . The concentrated labeling solution of the simple manganese compound is diluted with distilled water in the necessary proportions, for example to obtain a final concentration of manganese ions of 0.1 g / l. The beads of the same batch are immersed simultaneously in the diluted manganese marking solution for a time ranging from 1 to 5 hours (depending on the marking solution and the size of the beads). During this time a gentle agitation is maintained. The pH is maintained at the required value, for example about 5.5. After the required time, all the beads are rinsed with distilled water. After drying in dry air, the marking process is completed and the batch of beads is marked.

EXAMPLE 2 Method for Labeling Pearl of Culture by Samarium Sm ²⁺ ions

A concentrated solution of samarium Sm ²⁺ ions is prepared so as to obtain a concentration of 100 g / l of SmCl ₂ . The concentrated labeling solution of the simple samarium compound is diluted with distilled water in the necessary proportions, for example to obtain a final concentration of samarium ions of 0.1 g / l. The beads of the same batch are immersed simultaneously in the diluted samarium marking solution for a time ranging from 1 to 5 hours (depending on the marking solution and the size of the beads). During this time a gentle agitation is maintained. The pH is maintained at the required value, for example about 5.5. After the required time, all the beads are rinsed with distilled water. After drying in dry air, the marking process is completed and the batch of beads is marked.

EXAMPLE 3 Process for labeling cultured pearls by a combination of rare earth ions europium Eu ³⁺ / samarium Sm ³⁺

A mixed concentrated labeling solution of europium Eu ^{2 + /} samarium Sm ²⁺ ions is prepared so as to obtain a concentration of 50 g / l of SmCl ₂ and 50 g / l of EuCl ₂ . The concentrated labeling solution of the mixed samarium / europium compound is diluted with distilled water in the necessary proportions, for example to obtain a concentration final samarium ion of 0.1 g / 1. The pearls of the same batch are immersed simultaneously in the diluted samarium / europium marking solution for a time ranging from 1 to 5 hours (depending on the marking solution and the size of the beads). During this time a gentle agitation maintained. The pH is maintained at the required value. After the required time, all the beads are rinsed with distilled water. After drying in dry air, the marking process is completed and the batch of beads is marked.

Example 4: Marked bead identification method

The bead whose marking is to be determined is placed on a suitable sample holder so that the emission generated by incident light beam striking the bead can be received by the detector. The emission is analyzed spectrally using a spectrofluorimeter. The device is tuned to the required conditions with a repetition rate of 100 Hz. The excitation slot is set to 20 nm and the emission slot is set to 10 nm to obtain sufficient spectral resolution. The analysis is then started using the software controlling the spectrofluorimeter. A dedicated computer interface analyzes the transmitted signal and generates a simple answer that can report whether the pearl has been marked or not and whether the marking corresponds to a range of quality, a source, or other criteria defined beforehand.

Example 5: Washing tests on the beads after marking

It has been shown that the marking process is resistant to different types of washing, such as gentle washing with bleach, soapy water, sweat, water and alcohol. It is resistant to natural friction on the skin or textile but not polishing (mechanical abrasion). Holding simple over time or following a continuous washing with water for several days, for example 30 days, has shown that no change in the signal was made. Aging with alcohol at 45 ° for 48 hours does not cause any significant modification of the signal. Washing with soapy water (5% detergent) for 48 hours at room temperature does not cause any signal modification as well as washing in a dishwasher-like automated system (cycle 2 hours at 45 ° C). Aging in a 0.1% solution of active chlorine (bleach) or sweat at a rate of 1 ml / ct for 48 hours at ambient temperature induces a slight degradation of the signal, which nevertheless remains detectable. A degradation of the pearl is probably responsible for this drop in the signal. These tests in extreme conditions for cultured pearls confirm the very good behavior of the marking after normal chemical and physical aging.

Claims

A method of marking a solid comprising at least one mother-of-pearl coating, said method comprising immersing said solid in an aqueous solution comprising a photoluminescent tracer in the presence of said solid, for a time sufficient to obtain the fixing of said photoluminescent tracer to mother of pearl coating.

2. The method of marking according to claim 1, characterized in that said solid is a pearly pearl, preferably a pearl of culture produced by a pearl oyster, for example of the species Pinctada margaritifera.

3. A method of marking according to claim 1 or 2, characterized in that a plurality of solids is immersed simultaneously in the same bath of said aqueous solution, for example at least one pearl pearls.

4. A method of marking according to any one of claims 1 to 3, characterized in that said tracer is incorporated on a surface layer of the pearlescent coating with a thickness of at most 20 μιη, preferably at most 10 μιη.

5. Labeling method according to any one of claims 1 to 4, characterized in that said photoluminescent tracer is selected from those detectable by time resolved fluorescence in the presence of mother-of-pearl.

6. The method of marking according to any one of claims 1 to 5, characterized in that said light-emitting tracer is a rare earth ion, for example, a lanthanide.

7. The method of marking according to any one of claims 1 to 6, characterized in that said aqueous solution comprises a combination of at least two photoluminescent tracers.

8. A method of marking according to any one of claims 1 to 7, characterized in that said photoluminescent tracer is a lanthanide selected from Gd, Dy, Lu, Yb, Sm, Ho, Eu, Tb, Nd, Er or mixtures thereof, for example a combination of terbium and europium.

The labeling method according to any one of claims 1 to 8, wherein said aqueous solution comprises a combination of at least two photoluminescent tracers at different concentrations.

10. A solid comprising a nacre coating labeled according to the method of marking of any one of claims 1 to 9.

A pearlescent pearl comprising at least one tracer or a combination of photoluminescent tracers in a surface layer of the nacrière layer, said surface layer containing the tracer not exceeding 20 μιη in thickness, preferably at most ΙΟμιη, said photoluminescent tracer. being detectable vis-à-vis the natural photoluminescence emitted by said pearl pearl.

12. pearlescent pearl according to claim 11, characterized in that said photoluminescent tracer is a rare earth ion, preferably a lanthanide, for example gadolinium, europium or mixtures thereof.

13. A method of identifying a labeled solid according to claim 10 or a pearlescent pearl according to any one of claims 11 or 12, characterized in that it comprises the time resolved fluorescence detection of the tracer (s). photoluminescent.

14. The method of identification according to claim 13, characterized in that it further comprises the detection of absolute or relative amounts of a combination of photoluminescent tracers.

15. Detection means suitable for carrying out the method according to claim 13 or 14.

The detection means of claim 15 comprising a time resolved fluorescence detector and signal analysis means for identifying the presence of the photoluminescent tracer (s) in the labeled solid or pearl pearl.

17. Use of means according to claim 15 or 16, for tracing and / or identification of the production origin and / or the quality of a mother-of-pearl pearl, for example a cultured pearl produced by a pearl oyster. .