CH715365A2 - Substrate comprising a silver surface protected against tarnishing of silver and method of manufacturing such a substrate. - Google Patents

Abstract

The invention relates to a substrate (1) comprising a final silver surface (2) protected against tarnishing of silver by a protective layer (4) having a thickness of between 1 nm and 200 nm. Said protective layer (4) comprises a first layer (4a) of AI 2 O 3 deposited on said final silver surface and having a thickness of between 0.5 nm and 100 nm, and on the first layer (4a) of AI 2 O 3, a second layer (4b) of TiO 2 having a thickness of between 0.5 nm and 100 nm. The present invention also relates to a method of manufacturing such a substrate (1). The substrate (1) can be a timepiece dial.

Description

Field of the invention

The invention relates to a substrate comprising a final silver surface protected against tarnishing of silver by a protective layer. Such a substrate comprising a silver surface is in particular a timepiece, such as a dial, a wall lamp or a hand, which can be covered with a thin layer of silver. The present invention also relates to a method of manufacturing such a substrate.

Background of the invention

In the field of watchmaking, it is customary to produce a timepiece by covering a substrate with a thin layer of silver, preferably deposited by galvanic means, in order to give the timepiece the very white and unique appearance of silver. Such a timepiece is for example a dial, made of brass or gold, covered with a thin layer of silver.

[0004] However, silver has the drawback of tarnishing over time. To solve this problem, it is known to protect the sensitive silver surface of the timepiece by the zaponnage method. Zapon is a cellulose varnish dilutable in a solvent. Zaponnage is a process which consists of applying, for example by spraying, to the surfaces to be protected several layers of Zapon varnish, then passing them to the oven to accelerate their hardening. The final coating has a total thickness of approximately 8 to 15 µm.

However, this Zapon varnish only imperfectly protects sensitive metals. In addition, the necessary thickness of Zapon varnish deposited erases fine structuring details, such as the guilloché pattern frequently used to decorate a dial. As a result, the details of the guilloche are not highlighted, and may even disappear under the layers of varnish. Finally, the layers of Zapon varnish modify the color and appearance of the protected silver surface by varying the L * parameter (from the CIE L * a * b * color space).

To replace the zaponnage method, it has been proposed to deposit a protective layer on the sensitive silver surface by an ALD process, as described in patent EP 1 994 202. This process makes it possible to deposit a extremely thin coating (50 nm to 100 nm) and very protective, the protection obtained being greater than the protection obtained with a coating of typically 10 nm with Zapon.

However, this ALD method has the disadvantage that the use of an inadequate protective layer deposited on the silver surface of the substrate attenuates the shine and the color of the silver and modifies the aesthetic rendering of the silver surface. .

In addition, the ALD method also has the drawback of forming, on the silver surface of the substrate, a protective layer having poor adhesion to said silver surface, so that said protective layer deposited by ALD delaminates with the less stress, for example during final decoration operations by pad printing or other.

Summary of the invention

The present invention aims to remedy these drawbacks by providing a substrate having a silver surface effectively protected against tarnishing of silver while preserving the final appearance of said silver surface, and in particular the shine and the color of silver.

To this end, the invention relates to a substrate comprising a final silver surface protected against tarnishing of silver by a protective layer having a thickness between 1 nm and 200 nm.

According to the invention, said protective layer comprises a first layer of AI2O3deposited on said final silver surface and having a thickness of between 0.5 nm and 100 nm, and on the first layer of AI2O3, a second layer of TiO2 present a thickness between 0.5 nm and 100 nm.

The present invention also relates to a method for manufacturing such a substrate comprising a final silver surface protected against tarnishing of silver by a protective layer, said method comprising the following steps: <tb> a) <SEP> have a substrate with a final silver surface <tb> b) <SEP> depositing on at least part of said final silver surface of step a) at least one silver tarnish protection layer having a thickness of between 1 nm and 200 nm, said step b) comprising a first step b1) of depositing, on at least part of said final silver surface of step a), a first layer of Al2O3 having a thickness of between 0.5 nm and 100 nm, and a second step b2) of deposition, on the first layer of AI2O3 obtained in step b1), of a second layer of TiO2 having a thickness of between 0.5 nm and 100 nm.

Surprisingly, the order and thickness of the first layer of AI2O3 and the second layer of TiO2 allow to obtain a protective layer against tarnishing of silver which enhances the very white color as much as possible. silver, thus preserving the silvery luster of the final surface of the substrate.

Brief description of the drawings

Other features and advantages will clearly match the description given below, by way of indication and in no way limitative, with reference to the appended drawings, in which: <tb> fig. 1 <SEP> is a schematic view of a first variant of a substrate according to the present invention; <tb> fig. 2 <SEP> is a schematic view of a second variant of a substrate according to the present invention; and <tb> fig. 3 <SEP> is a schematic view of a third variant of a substrate according to the present invention.

Detailed description of preferred embodiments

The present invention relates to a substrate comprising a final silver surface protected against tarnishing of silver by a protective layer.

Such a substrate is for example a timepiece or jewelry item, and in particular a timepiece cladding element. In particular, the substrate may be a dial of a timepiece, which may have on its surface a structure, such as a guilloche, that is to say a set of lines with fine details, which intersect in order to obtain a decorative effect. The substrate can also be an index, a decoration attached to the dial (moon phase or other), or even a hand.

The substrate is preferably metallic. It can be made of brass, based on gold, yellow or white, or silver, or any other metal or metallic alloy, precious or not, suitable.

The substrate may or may not have an initial silver surface.

The substrate may include an initial silver surface, said substrate then being based on silver (pure silver or silver alloy, in particular silver alloys with an Ag content> 90% by weight) and intrinsically having said initial silver surface also forming the final silver surface. The protective layer is then deposited directly on the silver-based substrate.

Referring to FIG. 1, a substrate 1 is shown according to a first variant of the invention according to which the substrate 1 can be without an initial silver surface or comprise an intrinsic silver surface. In the first case, the substrate may for example be made of brass, based on gold, yellow or white, or any other metal or metallic alloy, precious or not, suitable for the exception of silver. In the second case, the substrate 1 is based on silver, in solid silver for example, and intrinsically has an initial silver surface.

Advantageously, the substrate 1 comprises a layer 2 of an alloy of silver and copper comprising between 0.1% and 10% by weight of copper relative to the total weight of the alloy, forming said final silver surface. The layer 2 of silver and copper alloy can be deposited directly on the substrate 1, in particular when said substrate 1 is not based on silver, and can replace the coating of fine silver traditionally used. The layer 2 of silver and copper alloy can be deposited by any suitable process, such as PVD (flash deposit), or galvanically by means of a suitable silver and copper galvanic bath.

Referring to FIG. 2, a substrate 10 is shown according to a second variant of the invention according to which the substrate 10 is not based on silver and comprises a layer 20 of substantially pure silver forming said final silver surface. Such a layer 20 is preferably deposited galvanically. The substrate 10 can itself be made of brass and covered with a layer of precious metal, for example deposited galvanically, for example a layer of gold. The substrate 10 can also be made of solid precious metal, for example solid gold. If necessary, intermediate metallic layers known to those skilled in the art can be used in order to avoid any intermetallic diffusion between certain metals initiated by heat treatments or the ALD process.

Referring to FIG. 3, a substrate 100 is shown according to a third variant of the invention according to which the substrate 100 is not silver-based and comprises a layer 2 of an alloy of silver and copper comprising between 0.1 % and 10% by weight of copper relative to the total weight of the alloy forming said final silver surface. In addition, the substrate 100 comprises, between said substrate 100 and said layer 2 of silver and copper alloy, a layer 20 of substantially pure silver.

Whatever the variant with a layer of substantially pure silver, said layer 20 of substantially pure silver may have a thickness of between 200 nm and 3000 nm.

According to one embodiment, the layer 20 of substantially pure silver may have a thickness between 200 nm and 600 nm, preferably between 300 nm and 500 nm in order to form a coating of fine silver.

According to another embodiment, the layer 20 of substantially pure silver can have a thickness of between 1000 nm and 3000 nm, preferably between 1500 nm and 2500 nm in order to constitute a coating of thick silver.

Such a thick silver coating has the advantage of obtaining an intermediate or final layer of substantially pure silver free of porosities, in order to be able to obtain a final silver surface of the substrate without porosity and thus ensuring increased adhesion of the silver tarnish protection layer on said final silver surface.

Whatever the variant with a layer of silver and copper alloy, layer 2 of silver and copper alloy preferably has a thickness between 200 nm and 600 nm, more preferably between 300 nm and 400 nm.

Preferably, the silver and copper alloy comprises between 0.2% and 8% by weight, preferably between 0.5% and 7% by weight, of copper relative to the total weight of the alloy. The proportion of copper relative to silver is chosen so as to create enough Cu radicals on the surface which will then ensure the adhesion of the protective layer against tarnishing of silver, without altering the color of the silver. since the layer of silver and copper alloy forms the final silver surface of the substrate.

The final silver surface of the substrate, either the silver and copper alloy layer 2 of the substrate 1 or 100, or the substantially pure silver layer 20 of the substrate 10, or the initial silver surface of the substrate if it is itself silver-based, is protected against tarnishing of silver by a protective layer 4 having a thickness between 1 nm and 200 nm, preferably between 1 nm and 100 nm, and more preferably between 40 nm and 100 nm.

According to the invention, said protective layer 4 comprises a first layer 4a of AI2O3 deposited on said final silver surface and having a thickness between 0.5 nm and 100 nm, preferably between 0.5 nm and 50 nm, and on the first layer 4a of Al2O3, a second layer 4b of TiO2 having a thickness between 0.5 nm and 100 nm, preferably between 0.5 nm and 50 nm.

In a particularly preferred manner, the first layer 4a of AI2O3 has a thickness between 30 nm and 50 nm and the second layer 4b of TiO2 has a thickness between 10 nm and 50 nm.

Advantageously, the protective layer 4 was deposited by a method chosen from the group comprising an ALD deposit (Atomic Layer Deposition), PVD (Physical Vapor Deposition), CVD (Chemical Vapor Deposition), and sol -gel. Preferably, the protective layer 4 has been deposited by ALD. A successive ALD deposition of the first layer 4a of AI2O3 then of the second layer 4b of TiO2 makes it possible to form compact layers and to obtain extremely thin and very protective coatings, with a particularly good aesthetic rendering. The details and parameters of such an ALD repository are known to those skilled in the art. They are for example described in patent EP 1 994 202. The layer AI2O3 can be obtained from a TMA precursor (Tri-Methyl-Aluminum) whose oxidation can be carried out with H2O, O2; or O3. The TiO2 layer can be obtained from TTIP (Titanium Iso ProPoxide) or else from TiCl4 (Tri Titanium Chloride), the oxidation of which can be carried out with H2O, O2 or O3.

In a particularly preferred manner, the layer 4 of protection against tarnishing of silver is obtained by an ALD deposition of a first layer of AI2O3 having a thickness of between 30 nm and 50 nm and of a second layer 4b of TiO2 having a thickness between 10 nm and 50 nm.

Surprisingly, the combination of the order and the thickness of the first layer of AI2O3 and of the second layer of TiO2 allows to obtain a layer of protection against tarnishing of silver which enhances as much as possible. the very white color of the silver, thus preserving the silvery luster of the final surface of the substrate.

The substrate of the invention is obtained by a manufacturing process which comprises the following steps: <tb> a) <SEP> provide a substrate 1, 10, 100 having a final silver surface <tb> b) <SEP> deposit on at least part of said final silver surface of step a) at least one layer 4 of protection against tarnishing of silver having a thickness of between 1 nm and 200 nm , preferably between 1 nm and 100 nm, and more preferably between 40 nm and 100 nm, said step b) comprising a first step b1) of deposition, on at least part of said final silver surface of step a) , a first layer 4a of AI2O3 having a thickness between 0.5 nm and 100 nm, preferably between 0.5 nm and 50 nm, and a second step b2) of deposition, on the first layer 4a of AI2O3 obtained at step b1), a second layer 4b of TiO2 having a thickness between 0.5 nm and 100 nm, preferably between 0.5 nm and 50 nm.

In a particularly preferred manner, the first layer 4a of AI2O3 has a thickness of between 30 nm and 50 nm and the second layer 4b of TiO2 has a thickness of between 10 nm and 50 nm.

Advantageously, step b) is carried out by a method chosen from the group comprising an ALD, PVD, CVD, and sol-gel deposit.

In a particularly preferred manner, step b) is carried out by ALD deposition.

Advantageously, the method of the invention can combine deposition of protective layers and plasma treatment, before and / or after step b2), typically an Ar plasma, in order to reduce the internal stresses of the deposited protective layers. This combination makes it possible to soften the protective layers to make them less brittle during environmental stresses, such as mechanical, thermal or others.

Advantageously, the method of manufacturing the substrate of the invention may comprise, between step a) and step b), at least one step c) of plasma pretreatment of the final silver surface of the substrate obtained at step a).

This step c) of plasma pretreatment consists in stripping the final silver surface of the substrate in order to eliminate in particular the AgS / Ag2S sulphides which have formed naturally on the surface of the substrate exposed to the air and which prevent good adhesion of the protective layer 4.

Advantageously, this step c) consists of a pretreatment by Ar plasma or Ar / H2 plasma.

According to one mode of implementation of the process for manufacturing the substrate of the invention, step b) is implemented directly after step c), without any further pretreatment.

According to another embodiment, the method of manufacturing the substrate of the invention comprises an intermediate step d) complementary, between step c) and step b), of oxidative pretreatment, making it possible to create AgO / Ag2O sites forming covalent bonds between the AI2O3 present in the first layer 4a and the silver of the final silver surface of the substrate so as to promote the adhesion of the protective layer 4 on the substrate.

Alternatively, the oxidative pretreatment of step d) may consist of a pretreatment by oxidizing plasma with an oxidizing agent such as oxygen, or Ar / O2, making it possible to create the AgO / Ag2O sites.

The dosage of O2 in plasma must be precise in order to create enough AgO / Ag2O sites, but which tend to yellow the silver, while guaranteeing the whiteness of the silver.

The plasma treatment parameters are known to those skilled in the art and do not require further details here.

According to another variant, the oxidizing pretreatment of step d) can consist of injecting water or liquid hydrogen peroxide into a vacuum pretreatment chamber causing the vaporization of the water or of the hydrogen peroxide, which in contact with the substrate, will form the AgO / Ag2O sites. The amount of water or hydrogen peroxide injected is of the order of a few tens of micromoles.

In a particularly advantageous manner, step d) is carried out without venting between step c) and said step d). To this end, the substrate pretreated according to step c) undergoes the additional pretreatment according to step d) without breaking the vacuum.

In addition, the substrate from step a) and pretreated according to step c) only or according to steps c) and d) is then advantageously transferred under vacuum to a deposition chamber, preferably by ALD deposition , for direct implementation of step b) on the pretreated substrate from step c) or steps c) and d), without venting the final silver surface of the substrate.

To this end, steps c) and d) of pretreatment and step b) of depositing the protective layer, preferably by ALD deposition, are advantageously implemented in the same overall processing machine in which the pretreatment device according to step c) or according to steps c) and d) is integrated into the device for depositing the protective layer 4, preferably by ALD deposition, allowing overall treatment without venting the final silver surface of the substrate, and preferably under vacuum, for the implementation of steps c), optionally d) if present, and b).

The substrate 1, 10, 100 of step a) is metallic, and preferably based on gold or silver.

Said substrate of step a) may comprise an initial silver surface, said substrate then being based on silver and intrinsically having said initial silver surface also forming the final silver surface. The protective layer 4 is then deposited directly on the silver-based substrate according to step b).

According to another alternative embodiment, if the substrate is made of solid silver, its color will not be as white as that of fine silver, it would then be possible to deposit, by electroplating or vacuum process, a layer of silver on solid silver, before depositing the protective layer

According to another variant, whether the substrate 1, 100 of step a) has or does not have an initial silver surface, the process for producing the substrate of the invention can comprise a step a1) of deposition on said substrate 1 , 100 of a layer 2 of a silver and copper alloy comprising between 0.1% and 10% by weight of copper relative to the total weight of the alloy to obtain said final silver surface, as shown in the fig. 1.

According to another variant, if the substrate 100 of step a) does not have an initial silver surface, the method for producing the substrate of the invention may comprise an intermediate step a2) of depositing a layer 20 substantially pure silver between said substrate 100 and the layer 2 of silver and copper alloy, as shown in FIG. 3.

According to another variant, if the substrate 10 of step a) does not have an initial silver surface, the method for producing the substrate of the invention can comprise a step a3) of depositing a layer 20 d substantially pure silver on said substrate 10 to obtain said final silver surface, as shown in FIG. 2.

Advantageously, the substrate 1, 10, 100 can be heat treated before at least one of steps a1), a2) or a3) and / or before step b) in order to relax any internal stresses linked in the previous machining or layer deposition steps. The temperatures and durations of treatments depend on the nature of the substrate and the layers and must not impact the aesthetics of the part before the deposition of the protective layer of step b). The thermal treatment parameters are known to those skilled in the art and do not require further details here.

Whatever the variant with a layer of substantially pure silver, said layer 20 of substantially pure silver has a thickness of between 200 nm and 3000 nm.

According to one embodiment, the layer 20 of substantially pure silver may have a thickness between 200 nm and 600 nm, preferably between 300 nm and 500 nm, in order to form a coating of fine silver.

According to another embodiment, the layer 20 of substantially pure silver may have a thickness of between 1000 nm and 3000 nm, preferably between 1500 nm and 2500 nm in order to constitute a coating of thick silver, as explained above.

Whatever the variant with a layer of silver and copper alloy, said layer 2 of silver and copper alloy preferably has a thickness between 200 nm and 600 nm, preferably between 300 nm and 400 nm.

Preferably, the alloy of silver and copper comprises between 0.2% and 8% by weight, preferably between 0.5% and 7% by weight, of copper relative to the total weight of the alloy.

When the substrate has a structure on its surface, such as a guilloche, step a) of the process for manufacturing the substrate of the invention comprises a sub-step according to which said structuring is carried out on the surface of the substrate. .

A substrate comprising a final silver surface protected by a protective layer according to the invention, in particular when the protective layer against tarnishing of silver has been deposited by ALD, has a very white appearance and luster of money preserved despite the presence of the silver tarnish protection layer. If the substrate has been guilloche, the fine details of the guilloche are clearly visible despite the presence of said protective layer against tarnishing of silver.

In addition, the substrate of the invention has a layer of protection against tarnishing of silver without defect in adhesion.

The substrates of the invention can also be used to produce jewelry, writing instruments, eyewear and leather goods.

Claims (42)

1. Substrate (1, 10, 100) comprising a final silver surface protected against tarnishing of silver by a protective layer (4) having a thickness between 1 nm and 200 nm, preferably between 1 nm and 100 nm, characterized in that said protective layer (4) comprises a first layer (4a) of AI2O3 deposited on said final silver surface and having a thickness between 0.5 nm and 100 nm, preferably between 0.5 nm and 50 nm and on the first layer (4a) of AI2O3, a second layer (4b) of TiO2 having a thickness between 0.5 nm and 100 nm, preferably between 0.5 nm and 50 nm. 2. Substrate according to claim 1, characterized in that the first layer (4a) of AI2O3 has a thickness between 30 nm and 50 nm and in that the second layer (4b) of TiO2 has a thickness between 10 nm and 50 nm . 3. Substrate according to one of claims 1 and 2, characterized in that the protective layer (4) has been deposited by ALD. 4. Substrate according to one of the preceding claims, characterized in that it is based on silver. 5. Substrate according to claim 4, characterized in that it comprises a layer (2) of an alloy of silver and copper comprising between 0.1% and 10% by weight of copper relative to the total weight of l alloy, forming said final silver surface. 6. Substrate according to one of claims 1 to 3, characterized in that said substrate is not based on silver and comprises a layer (20) of substantially pure silver forming said final silver surface. 7. Substrate according to one of claims 1 to 3, characterized in that said substrate is not based on silver and comprises a layer (2) of an alloy of silver and copper comprising between 0.1 % and 10% by weight of copper relative to the total weight of the alloy forming said final silver surface. 8. Substrate according to claim 7, characterized in that said substrate comprises, between said substrate and said layer (2) of silver and copper alloy, a layer (20) of substantially pure silver. 9. Substrate according to one of claims 6 or 8, characterized in that the layer (20) of substantially pure silver has a thickness between 200 nm and 3000 nm. 10. Substrate according to claim 9, characterized in that the layer (20) of substantially pure silver has a thickness between 200 nm and 600 nm, preferably between 300 nm and 500 nm. 11. Substrate according to claim 9, characterized in that the layer (20) of substantially pure silver has a thickness between 1000 nm and 3000 nm, preferably between 1500 nm and 2500 nm. 12. Substrate according to one of claims 5 and 7, characterized in that the layer (2) of silver and copper alloy has a thickness between 200 nm and 600 nm, preferably between 300 nm and 400 nm . 13. Substrate according to one of claims 5 and 7, characterized in that the silver and copper alloy comprises between 0.2% and 8% by weight, preferably between 0.5% and 7% by weight , of copper relative to the total weight of the alloy. 14. Substrate according to one of the preceding claims, characterized in that the substrate (1, 10, 100) is a timepiece. 15. Substrate according to one of the preceding claims, characterized in that it has a surface structure. 16. A method of manufacturing a substrate (1, 10, 100) comprising a final silver surface protected against tarnishing of silver by a protective layer (4), characterized in that said method comprises the following steps: a) provide a substrate (1, 10, 100) having a final silver surface b) depositing on at least part of said final silver surface of step a) at least one layer (4) of protection against tarnishing of silver having a thickness of between 1 nm and 200 nm, preferably between 1 nm and 100 nm, said step b) comprising a first step b1) of deposition, on at least part of said final silver surface of step a), of a first layer (4a) of AI2O3 having a thickness of between 0.5 nm and 100 nm, preferably between 0.5 nm and 50 nm and a second step b2) of deposition, on the first layer (4a) of AI2O3 obtained in step b1), of a second layer ( 4b) of TiO2 having a thickness between 0.5 nm and 100 nm, preferably between 0.5 nm and 50 nm. 17. Method according to claim 16, characterized in that the first layer (4a) of AI2O3 has a thickness between 30 nm and 50 nm and in that the second layer (4b) of TiO2 has a thickness between 10 nm and 50 nm . 18. Method according to one of claims 16 and 17, characterized in that step b) is carried out by a method chosen from the group comprising an ALD, PVD, CVD, and sol-gel deposit. 19. Method according to claim 18, characterized in that step b) is carried out by ALD deposition. 20. Method according to one of claims 16 to 19, characterized in that it comprises, before and / or after step b2), a plasma treatment step. 21. Method according to one of claims 16 to 20, characterized in that it comprises, between step a) and step b), at least one step c) of plasma pretreatment of the final silver surface of the substrate obtained in step a). 22. The method of claim 21, characterized in that step c) of plasma pretreatment consists of a pretreatment by Ar plasma or Ar / H2 plasma. 23. Method according to one of claims 21 and 22, characterized in that step c) is carried out without venting the final silver surface of the substrate between step c) and said step b). 24. Method according to one of claims 21 and 22, characterized in that it comprises, between step c) and step b), a step d) of oxidative pretreatment. 25. The method of claim 24, characterized in that step d) of oxidative pretreatment consists of a plasma pretreatment with an oxidizing agent. 26. The method of claim 24, characterized in that step d) of oxidative pretreatment consists in injecting liquid water or hydrogen peroxide into a vacuum pretreatment chamber. 27. The method of claims 24 to 26, characterized in that step d) is carried out without venting the final silver surface of the substrate between step c) and said step d). 28. Method according to claims 24 to 27, characterized in that step b) is carried out without venting the final silver surface of the substrate between step d) and said step b). 29. Method according to claim 28, characterized in that steps c), d) and b) are implemented in one and the same overall processing machine. 30. Method according to one of claims 16 to 29, characterized in that the substrate (1, 100) of step a) may or may not have an initial silver surface, and in that said method comprises a step a1) of depositing on said substrate (1, 100) a layer (2) of an alloy of silver and copper comprising between 0.1% and 10% by weight of copper relative to the total weight of the alloy to obtain said final silver surface. 31. A method according to claim 30, characterized in that the substrate (100) of step a) does not have an initial silver surface, and in that said method comprises an intermediate step a2) of depositing a layer ( 20) of substantially pure silver between said substrate (100) and the layer (2) of silver and copper alloy. 32. Method according to one of claims 16 to 29, characterized in that the substrate (10) of step a) does not have an initial silver surface, and in that said method comprises a step a3) of depositing 'a layer (20) of substantially pure silver on said substrate (10) to obtain said final silver surface. 33. Method according to claims 30, 31 and 32, characterized in that it comprises, before at least one of steps a1), a2) or a3) and / or before step b), a processing step thermal of the substrate (1, 10, 100) to relax any internal stresses in said substrate (1, 10, 100). 34. Method according to one of claims 16 to 29, characterized in that the substrate of step a) comprises an initial silver surface, said substrate being based on silver and intrinsically having said initial silver surface also forming the surface silver finish. 35. Method according to one of claims 16 to 34, characterized in that the substrate (1, 10, 100) is metallic, and preferably based on gold or silver. 36. Method according to one of claims 31 and 32, characterized in that the layer (20) of substantially pure silver has a thickness between 200 nm and 3000 nm. 37. The method of claim 36, characterized in that the layer (20) of substantially pure silver has a thickness between 200 nm and 600 nm, preferably between 300 nm and 500 nm. 38. The method of claim 36, characterized in that the layer (20) of substantially pure silver has a thickness between 1000 nm and 3000 nm, preferably between 1500 nm and 2500 nm. 39. Method according to one of claims 30 and 31, characterized in that the layer (2) of silver and copper alloy has a thickness between 200 nm and 600 nm, preferably between 300 nm and 400 nm . 40. Method according to one of claims 30 and 31, characterized in that the silver and copper alloy comprises between 0.2% and 8% by weight, preferably between 0.5% and 7% by weight , of copper relative to the total weight of the alloy. 41. Method according to one of claims 16 to 40, characterized in that the substrate (1, 10, 100) is a timepiece. 42. Method according to claim 41, characterized in that a structuring is carried out on the surface of the substrate (1, 10, 100).