The present invention relates to a rose gold alloy, a method of galvanic electroplating that can be used to obtain it, and its use for decorative plating and the production of self-supporting shells in the clothing, jewelry, costume jewelry, footwear and leather goods sectors.

As is known, the methods of galvanic electroplating make it possible to deposit one or more metals on an object that is capable of conducting electric current, thus forming one or more layers of various thickness.

In more detail, in some applications the end product that it is desired to obtain comprises both the object itself and the metallic layer, covering the former. Sometimes however, the deposition is extended appropriately over time until a layer is obtained that, in addition to having a considerable thickness and being an exact replication of the object (matrix) on which it has been deposited, is detached from the latter at the end of the method. The layer therefore constitutes a form of self-supporting shell (with the matrix removed) and in such case, as is known, the method is referred to as "electroforming". It is likewise well known that such baths have the peculiar characteristic of quickly and efficiently depositing a layer with a uniform thickness, both on the parts that protrude and in the recesses and in the hollows, thus ensuring metal coverings that are very bright but are not flattened out (which otherwise would render small details indistinguishable).

In the sector of gold alloys for galvanic electroplating, the rose gold alloy is known, which is currently identified by UNI standard EN ISO 8654:2018 by the title“Jewelry - Colors of gold alloys - Definition, range of colors and designation” with the code 4N-6N.

Such alloy, which can be used for decorative plating and/or for electroforming in the clothing, jewelry, costume jewelry, footwear and leather goods sectors with a carat weight comprised between 9 and 22 carats, typically comprises cadmium and indium as binding agents, in addition to gold, copper and zinc.

The principal drawback of such an alloy consists in that it loses its characteristics of brilliance, harmony, and weldability owing to the fact that the deposit is not perfectly uniform when the plating goes down to thicknesses of less than 100 micrometers.

In addition, even for greater thicknesses than those cited above, an alloy containing indium and cadmium has a certain degree of toxicity and the production of the alloy by way of galvanic electroplating leads to inconstant deposits, mainly owing to the fact that it is quite complicated to maintain the titer constant for the same current density applied.

In order to overcome the foregoing it is necessary to have deposits of high thicknesses, with an inevitable increase in the cost of the alloy which is directly linked to the amount of gold contained in it.

The aim of the present invention consists in providing a 4N-6N rose gold alloy by way of galvanic electroplating with optimal mechanical and weldability characteristics with a deposit thickness up to 50% reduced with respect to the thickness attainable with conventional alloys.

Within this aim, an object of the present invention consists in providing a 4N-6N rose gold alloy with no toxic metals and/or metalloids.

This aim and this and other objects which will become better evident hereinafter are achieved by a gold alloy, characterized in that it comprises gold, copper, zinc and tellurium with a percentage of tellurium expressed by weight on the total weight of the alloy comprised between 0.01 and 1%.

Furthermore, this aim and this and other objects which will become better evident hereinafter are achieved by a galvanic electroplating method for obtaining a gold alloy according to one or more of the preceding claims through the use of water-based galvanic baths, characterized in that it comprises the use of a galvanic bath comprising gold, copper, zinc and tellurium.

Further characteristics and advantages of the invention will become better apparent from the detailed description of a preferred, but not exclusive, embodiment of a gold alloy, according to the invention, that comprises gold, copper, zinc and tellurium, as a binding agent, with the following percentages expressed by weight on the total weight of the alloy:

- Au comprised between 30 and 95%

- Te comprised between 0.01 and 1%

- Cu comprised between 3% and 69.98%

- Zn comprised between 0.01% and 1%.

More specifically, such gold alloy comprises gold, copper, zinc and tellurium with the following percentages expressed by weight on the total weight of the alloy:

- Au comprised between 37% and 92%

- Te comprised between 0.02% and 0.2%

- Cu comprised between 7.6% and 62.97%

- Zn comprised between 0.01% and 0.2%.

In a specific embodiment, the gold alloy comprises gold, copper, zinc and tellurium with the following percentages expressed by weight on the total weight of the alloy:

- Au equal to 75%

- Te equal to 0.1%

- Cu equal to 24.88%

- Zn equal to 0.02%.

The gold alloy just described can be obtained with a method of galvanic electroplating by way of using water-based galvanic baths, in which these baths comprise gold, copper, zinc and tellurium with the following composition:

- Au comprised between 3 g/1 and 8 g/1 in the form of potassium dicyanoaurate complex,

- Cu comprised between 40 g/1 and 70 g/1 in the form of cuprous cyanide, - Zn comprised between 100 mg/1 and 1 g/1 in the form of a zinc (II) complex,

- Te comprised between 1 mg/1 and 100 mg/1 in the form of an alkaline complex,

and in which the operating parameters are:

- temperature comprised between 50 °C and 80°C,

- pH comprised between 8 and 12, and

- applied current density comprised between 0.2 A/dm ² and 1.5 A/dm ² .

Conveniently, the galvanic bath can be enriched with one or both of the substances selected from the group constituted by: free cyanide comprised between 10 g/1 and 50 g/1, complexing agents comprised between 5 g/1 and 20 g/1, conducting salts comprised between 10 g/1 and 100 g/1 and wetting agents comprised between 0.05 g/1 and 10 g/1.

More specifically, the complexing agents can be selected from the group constituted by: carboxylic acids, amino acids, polyamines, amines and phosphonic acids.

Considering the cited conducting salts and the wetting agents, these can be selected respectively from the group constituted by: citrates, tartrates, oxalates, gluconates, carbonates, phosphates and sulfates and from the group constituted by: lauryl sulfate and quaternary ammonium salts.

To complete the galvanic bath, it can comprise grain refiners and/or brighteners selected from the group of metals constituted by: Zr, Ir, Se, Sb, Sn, Ga, In, Ge, Bi, T1 and Ag and/or additional metals in trace amounts owing to the use of technical products for its production, which are comprised in the group of metals constituted by: Ag, As, Se, In, Ge and Ga.

Below is an example of a possible galvanic solution, and also the operating parameters of the galvanic bath:

- Au: 5 g/1

- Cu: 55 g/1

- Zn: 0.5 g/1 - Te: 50 mg/1

- pH: 10.5

- temperature: comprised between 60 and 70 °C

- current density: 0.5 A/dm ²

- triethylenetetramine: 1 ml/1

- iminodiacetic acid: 10 g/1

- sodium gluconate: 5 g/1

- free potassium cyanide: 25 g/1

In practice it has been found that the gold alloy and the method of galvanic electroplating, according to the invention, respond to the technical problem set out above by making possible a deposit having characteristics of brilliance, mechanical strength (with hardness comprised between 300 and 400 HV) and weldability that are comparable to the known art with a deposit thickness up to 50% reduced with respect to the thicknesses attainable with conventional alloys.

In other words, the possibility of obtaining gold alloys with very low thicknesses with unchanged mechanical characteristics enables a considerable cost saving both for the amount of gold used and for the subsequent processing stages, with reference to a work cycle based on electroforming.

With respect to other alloys obtained with the electroforming processes known today, excellent results are obtained in the welding and/or in the production of self-supporting shells even with thicknesses far below 100 microns, a lower limit value that to date could not be surpassed with the processes of the known art in order to obtain objects that have optimal characteristics of mechanical strength and harmony.

The alloy thus described and obtained can therefore be used for decorative plating and/or providing self-supporting shells in the clothing, jewelry, costume jewelry, footwear and leather goods sectors, obtaining thicknesses comprised between 1 and 1000 micrometers with carat weights from 9 to 22 carats.

An advantage of the gold alloy according to the present invention consists in that it is free from toxic metals and/or metalloids, such as cadmium, which for conventional alloys are essential as a binding agent.

The gold alloy, the method, and also the use, thus conceived, are susceptible of numerous modifications and variations, all of which are within the scope of the appended claims.

Moreover, all the details may be substituted by other, technically equivalent elements.

In practice, the materials used, as well as the contingent shapes and dimensions, may be any according to the requirements and to the state of the art.

The disclosures in Italian Patent Application No. 102019000001769 from which this application claims priority are incorporated herein by reference.

Where technical features mentioned in any claim are followed by reference signs, those reference signs have been included for the sole purpose of increasing the intelligibility of the claims and accordingly, such reference signs do not have any limiting effect on the interpretation of each element identified by way of example by such reference signs