JEWELLERY STONE, IN PARTICULAR FACETTED DIAMOND AND METHOD FOR MOUNTING SAME ON A MOUNT

Abstract

A jewelry stone, having a crown, a pavilion and an intermediate part between said crown and said pavilion, referred to as the girdle is disclosed. It has metal fastening means that are designed to allow it to be fastened to said mount, comprising a connecting zone located on said pavilion. The connecting zone is located on a part of or all of a limited-width peripheral sector of said pavilion, in which incident rays on the crown pass into the stone through an air/stone interface, are either reflected by a first pavilion/air interface at a point of the pavilion that is lower than said connecting zone, or are reflected entirely by said first pavilion/air interface of said stone in the peripheral sector having said connecting zone.

Claims

1. 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 said jewelry stone is mounted on a mount, said dorsal part being called pavilion and being separated from said crown by an intermediate part between said crown and said pavilion, called girdle, said jewelry stone including metal fastening means arranged to allow said jewelry stone to be fastened on said mount, said metal fastening means including a connecting zone located on said pavilion, wherein 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 (R3) on said crown penetrating said jewelry stone via an air/stone interface, are either reflected by a first pavilion/air interface on a point of said pavilion lower than said connecting zone or completely reflected by said first pavilion/air interface of said stone in said peripheral sector including said connecting zone, and are refracted to the outside of said jewelry stone, behind said pavilion, through at least one second pavilion/air interface of said jewelry stone.

2. The jewelry stone according to claim 1, wherein said peripheral sector is situated on said pavilion near said girdle.

3. The jewelry stone according to claim 1, wherein said peripheral sector includes a so-called invisible zone (ZI) in which no incident ray (R3) refracted at an air/crown interface is reflected by said first pavilion/air interface.

4. The jewelry stone according to claim 1, wherein said peripheral sector includes a band extending over 360 around the pavilion.

5. The jewelry stone according to claim 4, wherein said band covers a zone corresponding at least approximately to about 20 to 35% of the surface of said pavilion.

6. The jewelry stone according to claim 1, wherein said metal fastening means comprise a plurality of metal layers deposited in a sandwich.

7. The jewelry stone according to claim 6, wherein said plurality of metal layers comprises an inner layer forming a layer of carbide with said jewelry stone.

8. The jewelry stone according to claim 7, wherein said inner layer comprises titanium, tantalum, hafnium or niobium.

9. The jewelry stone according to claim 6, wherein said plurality of metal layers comprises an outer layer comprising the same material as that of the mount intended to receive said jewelry stone.

10. The jewelry stone according to claim 9, wherein said outer layer and said mount comprise gold.

11. The jewelry stone according to claim 6, wherein said plurality of metal layers comprises an intermediate layer forming a diffusion barrier between said inner layer and said outer layer.

12. The jewelry stone according to claim 11, wherein said intermediate layer comprises platinum.

13. The jewelry stone according to claim 1, wherein said metal fastening means are deposited using a physical vapor deposition (PVD) method.

14. A method for mounting a jewelry stone on a mount, said jewelry stone being 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 said jewelry stone is mounted on a mount, said dorsal part being called pavilion and being separated from said crown by an intermediate part between said crown and said pavilion, called girdle, said jewelry stone including metal fastening means arranged to allow said jewelry stone to be fastened on said mount, said metal fastening means including a connecting zone located on said pavilion, wherein said connecting zone is deposited over part or all of a peripheral sector of limited width of said pavilion, in which the incident rays (R3) on said crown penetrating said jewelry stone via an air/stone interface, are either reflected by a first pavilion/air interface on a point of said pavilion lower than said connecting zone or are completely reflected by said first pavilion/air interface of said stone in said peripheral sector including said connecting zone, and are refracted outside said jewelry stone, behind said pavilion, through at least one second pavilion/air interface of said jewelry stone.

15. The method according to claim 14, wherein said peripheral sector is defined at said pavilion near said girdle.

16. The method according to claim 14, wherein a band is deposited in said peripheral sector extending over 360 around said pavilion.

17. The method according to claim 14, wherein said band covers a zone corresponding to at least approximately 20 to 35% of the surface of said pavilion.

18. The method according to claim 14, wherein a plurality of metal layers are deposited in a sandwich to form said metal fastening means.

19. The method according to claim 18, wherein an inner layer is deposited forming a layer of carbide with said jewelry stone, said inner layer comprising titanium, tantalum, hafnium or niobium.

20. The method according to claim 18, wherein an outer layer is deposited comprising the same material as that of said mount intended to receive said jewelry stone.

21. The method according to claim 18, wherein an intermediate layer is deposited forming a diffusion barrier between an inner layer and an outer layer.

22. The method according to claim 14, wherein said metal fastening means are deposited using a PVD method.

23. The method according to claim 22, wherein said PVD method includes a PVD deposition done in an enclosure comprising an inert gas at a pressure between 10.sup.4 and 10.sup.2 mbar.

24. The method according to claim 14, wherein said jewelry stone is fastened to the mount by thermal compression.

25. The method according to claim 24, wherein said metal fastening means are compressed against said mount with a force of 2-20 kg/mm.sup.2 and at a temperature of 100-600 C. for a duration from 20 seconds to 60 minutes.

26. The method according to claim 25, wherein the compression temperature is 200-450 C.

27. The method according to claim 14, wherein said jewelry stone is fastened to said mount by welding.

28. The method according to claim 27, wherein said metal fastening means are welded against said mount with a force of 5-50 g/mm.sup.2 and a temperature of 280-350 C. for a duration from 1 second to 5 minutes.

29. The method according to claim 28, wherein a preform is used.

30. The method according claim 14, wherein a metal layer is deposited on the part of the surface of said mount intended to receive said jewelry stone before fastening of said jewelry stone.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] 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:

[0018] 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,

[0019] 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,

[0020] 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,

[0021] FIG. 4 is a side view of a stone according to the invention provided with said connecting zone, and

[0022] 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

[0023] 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.

[0024] 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.

[0025] As shown in particular in FIG. 1, depending on the size of the facets 11 of the stone 10, incident light rays R1, R2, 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 R1 that strikes a facet 11 of the crown 12 of the stone 10 at point A1, along an angle i.sub.1, relative to the normal H.sub.A1 to the incidence point A1 of the ray R1, 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.sub.1 of the air and the refraction index n.sub.2 of the stone 10 and the incident i.sub.1 and refracted i.sub.2 angles is written:

n.sub.1 sin(i.sub.1)=n.sub.2 sin(i.sub.2)

[0026] The refracted ray R1 is deviated by an angle i.sub.2 relative to the normal H.sub.A1, this angle i.sub.2 being smaller than the incident angle i.sub.1 of the incident ray R1, since the refraction index n.sub.1 of the air is lower than the refraction index n.sub.2 of the stone 10. This refracted ray R1 travels inside the stone 10 and strikes the wall of the pavilion 13, more specifically the first pavilion/air interface, at a point B1, on which it undergoes a complete reflection. Indeed, the refracted ray R1 forms an angle i.sub.r relative to the normal H.sub.B1 at the point B1 which is larger than the limit angle i.sub.l beyond which there is a total reflection and which obeys the law:

I.sub.l=arcsin(n.sub.1/n.sub.2).

[0027] For example, for a diamond stone 10 with a refraction index n.sub.2=2.42 and a refraction index of the air n.sub.1 equal to 1, the limit angle i.sub.l is substantially equal to 24. The reflected ray R1, along an angle i.sub.r at the point B1, is next sent onto a second pavilion/air interface point C1, where it undergoes a new total reflection, before being returned onto a third crown/air interface at a point D1. It undergoes a refraction such that the exit angle i.sub.4 is larger than the incident angle i.sub.3 at the point D1. It will be noted that the incident light at the point A1 of the crown 12 is returned to the point D1 of the crown 12 in the form of a ray R1, such that the stone 10 shines with all its brilliance, when the above conditions are met.

[0028] A second incident light beam R2 is shown in FIG. 1. The beam R2 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 A2. It penetrates the stone 10 and reaches the first pavilion/air interface, where it undergoes a first total reflection at point B2, then a second total reflection at point C2 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.

[0029] 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.

[0030] 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.

[0031] As an example and as shown in FIG. 2, an incident ray R3 is sent onto one of the facets 11 of the crown 12 of the stone 10 at an impact point A3, close to the girdle 14. It will be noted that the ray R3 is sent onto the facet 11 adjacent to the girdle 14. It penetrates the crown 12 in the form of a refracted ray R3 while coming close to the normal H.sub.A3 of the facet 11 at point A3 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 R3 undergoes a total reflection at point B3. 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 C3, under an angle smaller than the limit angle i.sub.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.

[0032] A second ray R4 shown in FIG. 2 is refracted at an impact point A4 on the crown 12, refracted while penetrating the stone 10 in the form of a ray R4 that is reflected on the first pavilion/air interface, below the metal band 22, at point B4. After its total reflection, it strikes the second pavilion/air interface, which is opposite the first pavilion/air interface, at a point C4 where it undergoes a second total reflection at point C4. It is next reflected toward the crown 12, which it traverses at point D4 while undergoing refraction. The ray R4 rejoins, regarding its optical trajectory, the rays R1 and R2 of FIG. 1 and returns the incident light while contributing to giving shine to the stone 10. This ray R4 not being reflected in the peripheral sector 131, it is visible by the viewer.

[0033] As illustrated by FIG. 3, the peripheral sector 131 also includes a so-called invisible zone ZI in which an incident ray R3 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.

[0034] 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.

[0035] 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.sup.4 to 10.sup.2 mbar.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] 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.sup.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.

[0040] According to another alternative, the stone is fastened to the mount by a welding machine under a force of 5-50 g/mm.sup.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

[0041] 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 R3 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.sub.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.

[0042] 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.

[0043] 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.