Patent Publication Number: US-2018042345-A1

Title: Jewellery stone, in particular facetted diamond and method for mounting same on a mount

Description:
TECHNICAL FIELD 
     The present invention relates to a jewelry stone, made from a natural or synthetic material, in particular a faceted diamond, including a visible frontal part called a crown and a dorsal part that is at least partially hidden when the stone is mounted on a mount, said dorsal part being called pavilion and being separated from the crown by an intermediate part between said crown and said pavilion, called girdle, said jewelry stone including fastening means allowing it to be fastened on said mount, said fastening means including a metal connecting zone located on said pavilion. 
     It also relates to a method for mounting a jewelry stone as defined above on a mount, said jewelry stone including fastening means arranged to allow it to be fastened on said mount, said fastening means including a metal connecting zone located on said pavilion. 
     BACKGROUND OF THE INVENTION 
     Jewelry stones, in particular diamonds, are intended to be fastened on a mount or frame, for example to form pieces of jewelry or timepieces. According to one known embodiment, stone fastening on a mount is done by depositing, on part of the peripheral surface of the stone, a metal coating allowing it to be closely secured to the mount by a welding, riveting or a similar method. 
     As an example, publication FR 2,042,156 A describes a jewelry stone having a pavilion on which a layer of metal is deposited. This metal layer makes it possible to weld the stone on a mount. However, such an arrangement has the drawback of not being aesthetically pleasing, since this metallized layer is visible due to the fact that certain incident rays, reflected by an exit interface of the stone situated in the metallized zone, are returned by the stone by total reflection and return the image of the metallized layer. 
     Publication JP 09173115 A describes a technique for fastening a jewelry stone, such as a diamond, on a mount, in which a first layer, for example an alloy containing titanium (Ti), copper (Cu), silver (Ag) and/or zirconium (Zr), is deposited on the diamond, and a second layer of metal is deposited on the mount, for example a gold (Au) alloy. The two layers of metal are next welded together to securely fasten the diamond on the mount. The metal layer is deposited on the pavilion of the diamond, more particularly, at the middle of the pavilion of the diamond and on a surface which is smaller than the total surface of the pavilion. For the same reasons as above, this technique has an aesthetic drawback, the layer of metal being visible when incident rays reflected in the stone at the metallized zone exit through the crown of the stone. 
     Publication WO 00/57743 A2 relates to a system making it possible to crimp a precious stone in a hollow jewelry item. The system includes a device used to create a metal fastening zone subjected to the surface of the precious stone and a connecting device serving to fasten the metal fastening zone on a shell of the hollow jewelry piece. To create the metal fastening zone, a circumferential part of the surface of the precious stone is metallized and a layer of metal is deposited by electrolysis on the metallized circumferential part of the surface of the precious stone. This fastening belt is formed in a groove hollowed in the stone and at least partially encroaches on the frontal part of the stone (i.e., the crown). 
     Publication WO 2014/030068 A2 relates to a frame that comprises a precious stone, a mounting surface and a brazed joint. The brazed joint is formed from a reactive metal alloy, this alloy allowing the adhesion of certain points on the surface of the precious stone directly to the mounting surface. However, the fastening techniques described in this publication risk not providing sufficiently reliable or effective maintenance of the stone, and the described brazing method requires high temperatures, generally exceeding 800° C., which consume considerable energy and may potentially damage a delicate mounting surface of a mount for a top-of-the-line piece. 
     The problems raised by fastening jewelry stones on a mount consist both of ensuring effective and reliable maintenance of the stone while not requiring high process temperatures for fastening, and performing this fastening practically invisibly, so as not to undermine the shine of the stone. The known techniques do not provide a satisfactory solution to these problems. 
     BRIEF DESCRIPTION OF THE INVENTION 
     The present invention aims to overcome the above drawbacks by proposing a jewelry stone arranged to be able to be fastened on its mount invisibly and a method for fastening the stone on its mount, the obtained fastening being effective, reliable, durable and invisible. 
     To that end, the invention relates to a jewelry stone as defined in the preamble, characterized in that said connecting zone is located on part or all of a peripheral sector with a limited width of said pavilion, in which the incident rays on the crown penetrating the stone by an air/stone interface, are either reflected by a first pavilion/air interface on a point of the pavilion lower than said connecting zone or completely reflected by said first pavilion/air interface of said stone in the peripheral sector including said connecting zone, and are refracted to the outside of said stone, behind said pavilion, through at least one second pavilion/air interface of said stone. 
     According to one preferred embodiment, said peripheral sector is situated on said pavilion near said girdle. Said peripheral sector can preferably include a so-called invisible zone in which no incident ray refracted at the air/crown interface is reflected by the first pavilion/air interface. Said peripheral sector can advantageously include a band extending over 360° around the pavilion. Said band preferably covers a zone corresponding at least approximately to about 20 to 35% of the surface of said pavilion. 
     Particularly advantageously, the metal fastening means can comprise a plurality of metal layers deposited in a sandwich. The plurality of metal layers preferably comprises an inner layer forming a layer of carbide with the stone. According to one advantageous embodiment, said inner layer comprises titanium, tantalum, hafnium or niobium. 
     The plurality of metal layers also preferably comprises an outer layer comprising the same material as that of the mount intended to receive the stone. Preferably, the outer layer and said mount comprise gold. According to another embodiment, the plurality of metal layers comprises an intermediate layer forming a diffusion barrier between said inner layer and said outer layer. The intermediate layer can comprise platinum. Advantageously, the metal fastening means are deposited using a PVD method. 
     Also to this end, the invention relates to a fastening method as defined in the preamble, characterized in that said connecting zone is deposited over part or all of a peripheral sector of limited width of said pavilion, in which the incident rays on the crown penetrating the stone via an air/stone interface, are either reflected by a first pavilion/air interface on a point of the pavilion lower than said connecting zone or are completely reflected by said first pavilion/air interface of said stone in the peripheral sector including said connecting zone, and are refracted outside said stone, behind said pavilion, through at least one second pavilion/air interface of said stone. 
     In the context of this method, said peripheral sector is advantageously defined at said pavilion near said girdle. Advantageously, a band is deposited in said peripheral sector that covers a zone corresponding to at least approximately 20 to 35% of the surface of said pavilion. The band advantageously covers a zone corresponding to at least approximately 20 to 35% of the surface of said pavilion. 
     In the context of the method, it is possible to deposit a plurality of metal layers in a sandwich to form the metal fastening means. It is also possible to deposit an inner layer forming a layer of carbide with the stone, this inner layer comprising titanium, tantalum, hafnium or niobium. It is also possible to deposit an outer layer comprising the same material as that of the mount intended to receive the stone before the fastening of said stone. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention and its advantages will better appear in the following description of one embodiment provided as a non-limiting example, in reference to the appended drawings, in which: 
         FIG. 1  is an axial sectional view of a stone schematically illustrating the trajectory of light rays penetrating the crown of said stone and returned by the crown after total reflection on the first and second pavilion/air interfaces, 
         FIG. 2  is an axial sectional view of a stone schematically illustrating the trajectory of light rays penetrating the crown of said stone provided with a connecting zone over a limited sector of the pavilion, 
         FIG. 3  is an axial sectional view of a stone schematically illustrating the trajectory of light rays penetrating the crown of said stone provided with a connecting zone in the invisible zone, 
         FIG. 4  is a side view of a stone according to the invention provided with said connecting zone, and 
         FIG. 5  is a bottom view of a stone according to the invention provided with said connecting zone. 
     
    
    
     ILLUSTRATIONS AND DETAILED DESCRIPTION OF THE INVENTION 
     The present invention relates to a jewelry stone, which will be referred to hereinafter as “stone”  10 . The stone  10  according to the invention can be natural or synthetic, and may in particular consist of a faceted diamond, but may also consist of an emerald, a sapphire, a ruby or another type of stone. In the illustrated examples, the stone  10  is a round diamond having multiple cut facets  11 . This example embodiment is of course not limiting, and the present invention refers to various shapes of stones. 
     In reference to figures, the stone  10 , as shown, includes a frontal part that is commonly called crown  12 , visible when the stone  10  is fastened on a mount (not shown). It is common for it to be cut so as to have multiple facets  11 . Behind the crown  12 , the stone  10  includes a dorsal part, commonly called pavilion  13 , that is defined relative to the crown  12  by an intermediate part, commonly called girdle  14 . The pavilion  13  is generally cut in a point and can also have multiple facets  11 . Typically, the pavilion  13  is at least partially hidden when the stone is mounted on its mount. Indeed, the pavilion  13  is typically used to allow fastening of the stone  10  on a mount such that only the crown  12  is visible, while making sure that the fastening of the stone  10  is as invisible as possible. One aim sought by jewelers is to hide the manner in which the stone  10  is fastened while ensuring that is fastened reliably and with optimal shine or brilliancy of the stone  10 , irrespective of the application, therefore independently of the type of mount, which may for example consist of a timepiece or a piece of jewelry. 
     As shown in particular in  FIG. 1 , depending on the size of the facets  11  of the stone  10 , incident light rays R 1 , R 2 , which penetrate the stone  10  through the crown  12 , can undergo one or several total reflections on the stone/air interfaces in the pavilion  13 , such that the incident light is returned through the stone/air interface of the crown  12  and imparts shine and the desired aesthetics to the stone  10 . For information, a ray R 1  that strikes a facet  11  of the crown  12  of the stone  10  at point A 1 , along an angle i 1 , relative to the normal H A1  to the incidence point A 1  of the ray R 1 , penetrates the stone  10  and undergoes a refraction phenomenon at the air/stone interface of the crown  12 . According to the Snell-Descartes law, the relationship that connects the refraction index n 1  of the air and the refraction index n 2  of the stone  10  and the incident i 1  and refracted i 2  angles is written: 
         n   1  sin( i   1 )= n   2  sin( i   2 ) 
     The refracted ray R′ 1  is deviated by an angle i 2  relative to the normal H A1 , this angle i 2  being smaller than the incident angle i 1  of the incident ray R 1 , since the refraction index n 1  of the air is lower than the refraction index n 2  of the stone  10 . This refracted ray R′ 1  travels inside the stone  10  and strikes the wall of the pavilion  13 , more specifically the first pavilion/air interface, at a point B 1 , on which it undergoes a complete reflection. Indeed, the refracted ray R′ 1  forms an angle i r  relative to the normal H B1  at the point B 1  which is larger than the limit angle i l  beyond which there is a total reflection and which obeys the law: 
         I   l =arcsin( n   1   /n   2 ). 
     For example, for a diamond stone  10  with a refraction index n 2 =2.42 and a refraction index of the air n 1  equal to 1, the limit angle i l  is substantially equal to 24°. The reflected ray R′ 1 , along an angle i r  at the point B 1 , is next sent onto a second pavilion/air interface point C 1 , where it undergoes a new total reflection, before being returned onto a third crown/air interface at a point D 1 . It undergoes a refraction such that the exit angle i 4  is larger than the incident angle i 3  at the point D 1 . It will be noted that the incident light at the point A 1  of the crown  12  is returned to the point D 1  of the crown  12  in the form of a ray R″ 1 , such that the stone  10  shines with all its brilliance, when the above conditions are met. 
     A second incident light beam R 2  is shown in  FIG. 1 . The beam R 2  penetrates substantially perpendicular to the central range  121  of the crown  12  while propagating in a straight line without undergoing any refraction at the incidence point A 2 . It penetrates the stone  10  and reaches the first pavilion/air interface, where it undergoes a first total reflection at point B 2 , then a second total reflection at point C 2  at the second pavilion/air interface. The light leaves substantially perpendicular to the central range  121  of the crown  12  without undergoing any refraction. As before, the incident light is returned after having followed a more or less complex optical path within the stone  10 . 
     Under the aforementioned conditions and assuming that the surface of the pavilion  13  is metallized or covered in part or in whole with an opaque coating, in order to arrange fastening means for fastening the stone  10  on a mount, at least part of the light having passed through the stone  10  and having been reflected by the surface provided with said opaque coating, returns the image of this opaque coating and undermines the desired brilliance of the stone  10 , which one is seeking to avoid. 
     To that end, the stone  10  according to the invention, as shown by  FIGS. 2 to 4 , is provided with metal fastening means  20  to allow it to be fastened on a mount (not shown). In this embodiment, these metal fastening means  20  include a connecting zone  21  situated on part or all of a limited peripheral sector  131  of the pavilion  13 . The metal fastening means  20  do not modify the normal journey of the light, but are positioned in the peripheral sector  131  such that they are made invisible. Indeed, the peripheral sector  131  of the pavilion  13  has particular optical properties that will be explained in the rest of the description. The connecting zone  21  can assume the form of a metal band  22  that extends completely, i.e., over 360°, around the pavilion, as illustrated in  FIG. 5 . The band  22  can be situated directly below the girdle  14 . The metal band  22  can be formed by a metal coating or layer that has a limited width relative to the height of the pavilion  13  and extends at least partially over the peripheral sector  131  of the pavilion  13 . As a result, the peripheral sector  131  can be partially or completely metallized, depending on the mount. Preferably, the peripheral sector  131  includes the metal band  22 , which covers a zone corresponding to 20 to 35% of the surface of the pavilion  13 . 
     As an example and as shown in  FIG. 2 , an incident ray R 3  is sent onto one of the facets  11  of the crown  12  of the stone  10  at an impact point A 3 , close to the girdle  14 . It will be noted that the ray R 3  is sent onto the facet  11  adjacent to the girdle  14 . It penetrates the crown  12  in the form of a refracted ray R′ 3  while coming close to the normal H A3  of the facet  11  at point A 3  and falls on the first pavilion/air interface of the pavilion  13  in the peripheral sector  131  where the metal band  22  is deposited. The ray R′ 3  undergoes a total reflection at point B 3 . Due to this total reflection, it is returned on the second pavilion/air interface of an opposite facet  11  of the pavilion  13  at point C 3 , under an angle smaller than the limit angle i l , which is the limit angle below which an incident ray no longer undergoes total reflection, but is refracted. This is the case for the ray reflected on the peripheral sector  131 , which is refracted upon leaving the stone  10  by the second pavilion/air interface of the pavilion  13 . Consequently, the peripheral sector  131  of the pavilion  13  has the particularity of not returning the light under conditions allowing a second total reflection on the second pavilion/air interface. As a result, the image of the metallized or opaque metal band  22  that is situated in this peripheral sector  131  is not visible at the front of the stone  10 , i.e., an observer will not see the connecting zone  21  of the stone  10 , since the metal band  22  serving as fastening means  20  will then not be visible upon observing the crown  12 . 
     A second ray R 4  shown in  FIG. 2  is refracted at an impact point A 4  on the crown  12 , refracted while penetrating the stone  10  in the form of a ray R′ 4  that is reflected on the first pavilion/air interface, below the metal band  22 , at point B 4 . After its total reflection, it strikes the second pavilion/air interface, which is opposite the first pavilion/air interface, at a point C 4  where it undergoes a second total reflection at point C 4 . It is next reflected toward the crown  12 , which it traverses at point D 4  while undergoing refraction. The ray R 4  rejoins, regarding its optical trajectory, the rays R 1  and R 2  of  FIG. 1  and returns the incident light while contributing to giving shine to the stone  10 . This ray R 4  not being reflected in the peripheral sector  131 , it is visible by the viewer. 
     As illustrated by  FIG. 3 , the peripheral sector  131  also includes a so-called invisible zone ZI in which an incident ray R 3  refracted at the air/crown interface can only be reflected by the first pavilion/air interface outside said invisible zone ZI. In other words, no ray is reflected in the invisible zone. This invisible zone ZI is situated below the girdle, and its height depends on the height of the girdle, which is typically 2-6% of the diameter of the stone. For example, with a stone  10  having a diameter of 2 mm, the width of the invisible zone of this alternative may be 0.25 mm. If one provides a metal band  22  narrow enough for it to be situated in this invisible zone ZI, then any incident ray at the air/crown interface will be reflected at the first pavilion/air interface outside the band  22 . As a result, the metal band  22  will not be visible, since no light ray will be able to reach the invisible zone. In this case, the connecting zone  21  including the band  22  does not completely cover the peripheral sector  131 . 
     As a result, the particular optical properties of the peripheral sector  131  make it possible to deposit the connecting zone  21  on part or all of this peripheral sector  131 , such that they are made invisible for a viewer looking at the stone  10  via the crown  12 . It has been observed in faceted round diamonds that the peripheral sector  131  is situated directly below the girdle  14  and extends over a surface smaller than the total surface of the pavilion  13 . 
     According to one embodiment of the present invention, the metal fastening means  20  are deposited on the surface of the stone using a PVD (Physical Vapor Deposition) method. The use of PVD makes it possible to form the connecting zone  21  in a controlled and precise manner on the surface of the stone. The PVD deposition step can be preceded by a step for cleaning the surface of the stone, as well as, optionally, depositing an adherence layer. Preferably, the PVD deposition step takes place in a chamber comprising an inert gas, such as argon, at a pressure between 10 −4  to 10 −2  mbar. 
     In one embodiment, the metal fastening means  20  comprise a plurality of metal layers deposited in a sandwich on the surface of the stone. According to one privileged alternative, an inner metal layer of titanium (or a titanium-based alloy) is deposited first on the stone, followed by an intermediate layer made from platinum (or a platinum-based alloy), then an outer layer of gold (or a gold-based alloy). Here, the layer of titanium, which preferably has a thickness of 40-500 nm, plays an adherence role, the titanium forming a layer of carbide with the stone. Other materials capable of forming a carbide layer with the stone (such as tantalum, hafnium or niobium) can alternatively be used in place of titanium as inner layer. The outer layer of gold, which preferably has a thickness of 100-2000 nm, allows fastening to a gold mount by welding or by thermocompression, as described below. Of course, if the mount intended to receive the stone is made from another material, the material of the outer layer can be adapted accordingly. The platinum layer, which preferably has a thickness of 60-500 nm, forms a diffusion barrier between the layer of titanium and the layer of gold, but other materials can also be used as intermediate layers. Other layers aside from those that have been mentioned may also be present in the fastening means  20 . 
     After the formation of the metal fastening means  20  on the surface of the stone, a chemical cleaning step can take place to eliminate any metal material present in unwanted locations in order to ensure that the connecting zone  21  is positioned correctly and is not discernible, as explained in detail above. 
     After metallization, the stone including the metal fastening means  20  can be fastened to a corresponding mount using different techniques, but is preferably fastened by thermocompression or welding. In the context of thermocompression, and preferably also in the context of welding, a metal layer is also formed by a PVD method on the part of the surface of the mount intended to receive the stone (and in particular the metal fastening means  20 ). In particular, for a gold mount, the metal layer deposited on the mount is preferably also made from gold. This deposition of a metal layer on the mount can also be preceded by a step for cleaning the surface of the mount in question. 
     According to one alternative, the stone is fastened to the mount by thermocompression, and the metal fastening means  20  comprising a gold outer layer are compressed against a gold layer deposited on the mount. In one example, a compression machine, operating at a force of 2-20 kg/mm 2  and at a temperature of 100-600° C. (or more preferably 200-450° C.) for a duration from 20 seconds to 60 minutes, is used for this step. 
     According to another alternative, the stone is fastened to the mount by a welding machine under a force of 5-50 g/mm 2  and a temperature of 280-350° C. for a duration from 1 second to 5 minutes. As indicated above, in this case, a pre-form of an appropriate material and having an appropriate shape (for example, a conical ring made from gold-tin) is used, and the mount preferably has a gold layer deposited beforehand on its surface. A chemical cleaning step can take place after the welding to eliminate any remaining debris. 
     Possibilities for Industrial Application 
     This description clearly shows that either the metal band  22  is not discernible because it is found in the invisible zone ZI just below the girdle, or all of the incident rays R 3  that are reflected by the peripheral sector  131 , at a first pavilion/air interface, in which the metal band  22  is situated, are returned on a second pavilion/air interface under an angle smaller than the total reflection limit angle i l , such that they are refracted and evacuated at the rear of the pavilion  13  of the stone  10  without being seen. The invention makes it possible to achieve the desired aims, i.e., making the connecting zone  21  of the stone  10  invisible when it is fastened to its mount. 
     Depositing metal fastening means  20  on the pavilion using a PVD method allows the formation of a metal connecting zone  21  with a controlled size and precise position. Preferably, this connecting zone  21  extends like a metal band  22  over 360° around the pavilion, which allows reliable and robust fastening to a mount, even if the stone is small and the band  22  has a relatively thin width. Furthermore, the stone including the metal fastening means  20  can advantageously be fastened to the mount according to conditions where the temperatures do not exceed 600° C., and more preferably do not exceed 450° C. 
     The present invention is not limited to the described example embodiment, but extends to any modifications and alternatives obvious for one skilled in the art.