TARNISHING RESISTANT QUINARY GOLD ALLOY, WITH COLOR COMPATIBLE WITH THE 5N STANDARD

Field of the invention

The present disclosure relates to the field of Gold alloys and in particular relates to a Gold alloy, quinary, having color compatible with the 5N standard.

The present disclosure also relates to a method of producing Gold alloys having color compatible with the 5N standard.

The Gold alloy and the Gold alloys production method according to the disclosure are an alloy and a Gold alloys production method for jewellery and watchmaking applications, respectively.

Backqround art

In the jewellery and watchmaking industry, Gold is not used in pure form because it is too ductile. For jewellery and watchmaking applications, Gold alloys are typically used for jewellery or watchmaking, which are characterized by a higher hardness with respect to Gold in pure form and/or with respect to Gold alloys with low hardness or high ductility.

It is well known that, generally, Gold alloys can undergo undesirable color changes over time, as a result of interactions with aggressive environments. These interactions lead to the formation of thin layers of reaction products, which remain adherent to the surface of the alloy, causing an alteration in color and gloss (document "Observations of onset of sulphide tarnish on gold-base alloys"; JPD, 1971 , Vol. 25, issue 6, p. 629-637).

The environments capable of promoting alterations in the color of Gold alloys are many and are related to their applications.

The standard colors for gold alloys can be univocally measured in the CIELAB 1976 color chart, which defines a color on the basis of a first parameter L ^* a second parameter a ^* and a third parameter b ^* where the first parameter L ^* identifies the brightness and assumes values between 0 (black) and 100 (white) while the second parameter a ^* and the third parameter b ^* represent chromaticity parameters. In particular, in the CIELAB 1976 color chart, the achromatic scale of greys is identified by the points wherein a ^* =b ^* =0; positive values for the second parameter a ^* indicate a color tending more towards red the more the value of the second parameter is high; negative values for the second parameter a* indicate a color tending more towards green the more the value of the second parameter a* is high in absolute value, even if negative; positive values for the third parameter b* indicate a color tending to yellow the more the value of the third parameter is high; negative values for the third parameter b* indicate a color tending to blue the more the value of the third parameter b* is high in absolute value, even if negative.

It is also possible to transform the second parameter a* and the third parameter b* into polar parameters defined as follows:

Cab* =7 (a * ² + b * ² )

The Cab* parameter is defined as "chroma"; the higher the value of the Cab* parameter is, the greater the color saturation will be; the lower the value of the Cab* parameter is, the lower the color saturation will be, which will tend towards the grey scale. To the Applicant's knowledge, alloys with a gold content higher than 750%o, which can be used as they are as white or grey gold alloys and do not require rhodium-plating surface treatments, arbitrarily have Cab* values<8. The parameter b* identifies instead the color shade. In particular, the ISO DIS 8654: 2017 standard defines seven color designations regarding Gold alloys for jewellery. In particular, these alloys are defined according to the following table, in which the color is defined on a standard reference named between ON and 6N. For the measurement of the color of an alloy, in particular, the ISO DIS 8654 standard makes it explicit that the measuring apparatus for measuring the color of a gold alloy must comply with to CIE Publication No. 15. In particular, such a measuring apparatus is a spectrophotometer with an integrating sphere, capable of measuring a reflection spectrum with a measurement geometry compatible with the designation di:8° or 8°:di (specular component included). The apparatus is adjusted according to the following parameters:

- specular component included - standard illuminating D65 at 6504 K

- standard observer 2°

The color measurement results from an average of 5 different measures of the sample, with repositioning, ensuring a pivoting between a measure and another. From the ISO DIS 8654: 2017 standard, the following table is extracted showing L* a* b* nominal values in trichromatic coordinates for 5N standard color alloys, including tolerances. From the standard it is therefore possible to obtain, within the CIE L*a*b* color space, a plurality of areas, each of which represents the color intervals within which it is possible to assert that an alloy has a color 0N...6N. This area related to 5N is shown in Figure 1.

The actual accuracy with which it is possible to measure the amounts of components of a Gold alloy, typically with precision higher than 0.1 ppt (one part each 10000) by weight, both before the melting of the alloy and afterwards (post casting analysis) allows the color to be identified with great precision. The ISO DIS 8654: 2017 standard also proposes recommended chemical compositions for each of the 0N-6N alloys. In particular, for the 5N coloration, the recommended chemical compositions are as shown in the following table:

The Applicant has observed that the 5N Gold alloy exhibits a substantial color instability, particularly when exposed to environments wherein chlorides or sulphides are present.

Variations of the color of a Gold alloy according to the color as defined on the CIE 1976 color chart and specified by the E=f (L* a* b*) coordinate, defined:

- L ^* ₀ as the first parameter under original conditions, at time to=0;

- a ₀ ^* as the second parameter in original conditions, at time to=0;

- bo as third parameter in original conditions, at time to=0; are defined by the following equation: It has also been observed that the human eye of a technician expert in precious materials is able to detect variations of color DE (L* a* b*) >1.

The 5N Gold alloy has a color that is highly valued in the jewellery industry, but its substantial color instability when exposed to chemically aggressive environments makes the jewellery objects that use it particularly delicate and not suitable for intensive use with perspiration or in a marine environment.

From PCT/IB2019/052092 are known Gold alloys, quaternary or quinary, alternatively comprising Platinum or Palladium. Also known from PCT/IB2019/052092 is an alloy, coded as LRS 494 alloy, distinguished by:

- Au in the amount equal to 791 %o by weight,

- Cu in the amount equal to 167%o by weight,

- Ag in the amount equal to 32%o by weight,

- Pd in the amount equal to 5%o by weight, and - Pt in the amount equal to 5%o by weight.

The Applicant at the time observed that the addition of Platinum in a Gold alloy, and in particular the replacement of determined parts of Palladium with Platinum, resulted in a tangible deterioration of performance in terms of color variation DE (L* a*, b*), particularly in Thioacetamide.

In the PCT/IB2019/052092 document emerged that, among the alloys with Gold content substantially equal to or lower than 833%o by weight, the alloy coded with LRS387, quaternary, comprising: Au, in the amount equal to 833%o by weight, Cu in the amount equal to 129%o by weight, Ag in the amount equal to 23%o by weight and Pd in the amount equal to 15%o by weight, had substantially the best performance in Thioacetamide and in air in terms of resistance to color change. LRS387 alloy is platinum-free.

In the PCT/IB2019/052092 document is also disclosed an alloy, coded with reference LRS494, in which Platinum and Palladium are present, each in the amount equal to 5%o by weight.

SUMMARY

An object of the present invention is to describe a quinary Gold-Copper- Silver-Palladium-Platinum alloy, suitable for use in jewellery applications and having high resistance to tarnishing.

To this purpose, the Applicant, according to an aspect of the present disclosure, has conceived a tarnishing resistant Gold alloy for jewellery, comprising:

- Gold in the amount comprised in the range [815-846] %o by weight,

- Copper in the amount comprised in the range [120-154] %o by weight,

- Silver in the amount comprised in the range [18-35] %o by weight,

- Platinum in the amount comprised in the range [1-10] %o by weight,

- Palladium in the amount comprised in the range [7-15] %o by weight, in which the Gold alloy is a quinary alloy.

According to a further non-limiting aspect, the so composed Gold alloy exhibits, under the conditions set forth in ISO DIS 8654:2017 standard, a color compatible with the color standard of 5N alloys. For the purposes of the present disclosure, a quinary alloy is defined as an alloy in which substantially only five elements are present, with the exclusion of undesirable impurities.

According to a further non-limiting aspect, the alloy according to the present disclosure consists of Gold, Copper, Silver, Platinum and Palladium in the following amounts:

- Gold in the amount comprised in the range [815-846] %o by weight,

- Copper in the amount comprised in the range [120-154] %o by weight,

- Silver in the amount comprised in the range [18-35] %o by weight,

- Platinum in the amount comprised in the range [1-10] %o by weight,

- Palladium in the amount comprised in the range [7-15] %o by weight.

A further object of the present invention is to describe a Gold alloy, suitable to be used in jewellery applications and having high resistance to tarnishing, which includes:

- Gold in the amount comprised in the range [815-846] %o by weight,

- Copper in the amount comprised in the range [120-154] %o by weight,

- Silver in the amount comprised in the range [18-35] %o by weight,

- Platinum in the amount comprised in the range [1-10] %o by weight,

- Palladium in the amount comprised in the range [7-15] %o by weight,

- Iridium and/or Ruthenium and/or Rhenium in a total amount not higher than 2%o by weight, optionally not higher than 1 %o by weight.

Further non-limiting aspects of the alloy according to the present disclosure are presented below.

According to a further non-limiting aspect, the sum of the weight amounts of Gold, Copper, Silver, Platinum and Palladium is equal to 1 000%o.

According to a further non-limiting aspect the tarnishing resistant Gold alloy for jewellery, comprises:

- Gold in the amount comprised in the range [815-846] %o by weight,

- Copper in the amount comprised in the range [125-137] %o by weight,

- Silver in the amount comprised in the range [18-35] %o by weight,

- Platinum in the amount comprised in the range [1-10] %o by weight,

- Palladium in the amount comprised in the range [7-15] %o by weight.

According to a further non-limiting aspect, the Gold alloy comprises Copper in the amount comprised in the range [125-137] %o by weight. According to a further non-limiting aspect, the Gold alloy comprises:

- Gold in the amount comprised in the range [815-840] %o by weight,

- Copper in the amount comprised in the range [125-137] %o by weight,

- Silver in the amount comprised in the range [18-35] %o by weight,

- Platinum in the amount comprised in the range [1-7] %o by weight,

- Palladium in the amount comprised in the range [7-15] %o by weight.

According to a further non-limiting aspect, the Gold alloy comprises:

- Gold in the amount comprised in the range [815-840] %o by weight,

- Silver in the amount comprised in the range [18-35] %o by weight,

- Platinum in the amount comprised in the range [1-7] %o by weight.

According to a further non-limiting aspect, the Gold alloy comprises:

- Gold in the amount comprised in the range [815-840] %o by weight,

- Copper in the amount comprised in the range [125-137] %o by weight,

- Silver in the amount comprised in the range [20-34] %o by weight,

- Platinum in the amount comprised in the range [1-7] %o by weight,

- Palladium in the amount comprised in the range [7-15] %o by weight.

According to a further non-limiting aspect, the Gold alloy includes:

- Silver in the amount comprised in the range [18-35] %o by weight.

According to a further non-limiting aspect, the Gold alloy comprises:

- Silver in the amount comprised in the range [20-34] %o by weight.

According to a further non-limiting aspect, the Gold alloy comprises:

- Gold in the amount comprised in the range [815-840] %o by weight,

- Copper in the amount comprised in the range [127-137] %o by weight,

- Silver in the amount comprised in the range [20-34] %o by weight.

According to a further non-limiting aspect, the Gold alloy comprises:

- Gold in the amount comprised in the range [827-839] %o by weight,

- Copper in the amount comprised in the range [127-132] %o by weight.

In a further non-limiting aspect, the Gold alloy comprises:

- Gold in the amount comprised in the range [827-839] %o by weight,

- Copper in the amount comprised in the range [127-132] %o by weight,

- Silver in the amount comprised in the range [20-34] %o by weight,

- Platinum in the amount comprised in the range [1-7] %o by weight,

- Palladium in the amount comprised in the range [7-15] %o by weight.

According to a further non-limiting aspect, the Gold alloy comprises: - Gold in the amount comprised in the range [830-836] %o by weight,

- Copper in the amount comprised in the range [127-132] %o by weight,

- Silver in the amount comprised in the range [20-34] %o by weight,

- Platinum in the amount comprised in the range [1-7] %o by weight,

- Palladium in the amount comprised in the range [7-15] %o by weight.

According to a further non-limiting aspect, the Gold alloy comprises:

- Platinum in the amount comprised in the range [1-6] %o by weight, and

- Palladium in the amount comprised in the range [8-13] %o by weight.

According to a further non-limiting aspect, the Gold alloy comprises:

- Gold in the amount comprised in the range [815-840] %o by weight,

- Copper in the amount comprised in the range [127-137] %o by weight,

- Silver in the amount comprised in the range [20-34] %o by weight,

- Platinum in the amount comprised in the range [1-6] %o by weight,

- Palladium in the amount comprised in the range [8-13] %o by weight.

According to a further non-limiting aspect, in the Gold alloy, the ratio by weight between Platinum and Palladium is comprised between ½ and ¼, preferably between 9/20 and ¼, more preferably between 4/10 and ¼.

According to a further non-limiting aspect, the Gold alloy comprises:

- Gold in the amount comprised in the range [815-840] %o by weight,

- Copper in the amount comprised in the range [127-137] %o by weight,

- Silver in the amount comprised in the range [20-34] %o by weight,

- Platinum in the amount comprised in the range [1-5] %o by weight,

- Palladium in the amount comprised in the range [9-12] %o by weight.

According to a further non-limiting aspect, the Gold alloy comprises:

- Gold in the amount comprised in the range [827-839] %o by weight,

- Copper in the amount comprised in the range [127-132] %o by weight,

- Silver in the amount comprised in the range [20-34] %o by weight,

- Platinum in the amount comprised in the range [1-5] %o by weight,

- Palladium in the amount comprised in the range [9-12] %o by weight.

According to a further non-limiting aspect, the Gold alloy comprises:

- Gold in the amount comprised in the range [830-836] %o by weight,

- Copper in the amount comprised in the range [127-132] %o by weight,

- Silver in the amount comprised in the range [20-34] %o by weight,

- Platinum in the amount comprised in the range [1-5] %o by weight, - Palladium in the amount comprised in the range [9-12] %o by weight.

According to a further non-limiting aspect, the Gold alloy comprises:

- Gold in the amount comprised in the range [815-825] %o by weight, in combination with:

- Copper in the amount comprised in the range [129-137] %o by weight.

According to a further non-limiting aspect, the Gold alloy comprises:

- Gold in the amount comprised in the range [815-825] %o by weight,

- Copper in the amount comprised in the range [129-137] %o by weight,

- Silver in the amount comprised in the range [30-34] %o by weight,

- Platinum in the amount comprised in the range [2-5] %o by weight,

- Palladium in the amount comprised in the range [8-13] %o by weight.

According to a further non-limiting aspect, the Gold alloy comprises:

- Silver in the amount comprised in the range [30-34] %o by weight.

According to a further non-limiting aspect, the Gold alloy comprises:

- Silver in the amount comprised in the range [31-33] %o by weight.

According to a further non-limiting aspect, the Gold alloy comprises:

- Gold in the amount comprised in the range [815-825] %o by weight,

- Copper in the amount comprised in the range [129-137] %o by weight,

- Silver in the amount comprised in the range [31-33] %o by weight,

- Platinum in the amount comprised in the range [2-5] %o by weight,

- Palladium in the amount comprised in the range [8-13] %o by weight.

According to a further non-limiting aspect, the Gold alloy comprises:

- Copper in the amount comprised in the range [132-136] %o by weight,

- Silver in the amount comprised in the range [31-33] %o by weight,

- Platinum in the amount comprised in the range [3-4] %o by weight,

- Palladium in the amount comprised in the range [10-11] %o by weight.

According to a further non-limiting aspect, the Gold alloy comprises:

- Gold in the amount comprised in the range [815-825] %o by weight,

- Copper in the amount comprised in the range [132-136] %o by weight,

- Silver in the amount comprised in the range [31-33] %o by weight,

- Platinum in the amount comprised in the range [3-4] %o by weight,

- Palladium in the amount comprised in the range [10-11] %o by weight.

According to a further non-limiting aspect, the Gold alloy comprises:

- Gold in the amount comprised in the range [832-834] %o by weight, - Silver in the amount comprised in the range [22-24] %o by weight,

- Copper in the amount comprised in the range [129-131] %o by weight,

- Platinum in the amount comprised in the range [2-4] %o by weight,

- Palladium in the amount comprised in the range [10-12] %o by weight.

According to a further non-limiting aspect, the Gold alloy comprises:

- Gold in the amount comprised in the range [819-821] %o by weight,

- Silver in the amount comprised in the range [31-33] %o by weight,

- Copper in the amount comprised in the range [133-135] %o by weight,

- Platinum in the amount comprised in the range [3-5] %o by weight,

- Palladium in the amount comprised in the range [9-11] %o by weight.

According to a further non-limiting aspect, the Gold alloy comprises:

- Gold in the amount comprised in the range [819-821] %o by weight,

- Silver in the amount comprised in the range [31-33] %o by weight,

- Copper in the amount comprised in the range [133-135] %o by weight,

- Platinum in the amount comprised in the range [2-4] %o by weight,

- Palladium in the amount comprised in the range [10-12] %o by weight.

According to a further non-limiting aspect, the Gold alloy has an initial hardness, without work hardening, equal to at least 125 points according to the HV5 measurement method, optionally equal to at least 128 points according to the HV5 measurement method, and/or has an initial hardness, without work hardening, of maximum 141 points according to the HV5 measurement method, optionally of maximum 139 points according to the HV5 measurement method.

According to a further non-limiting aspect, the Gold alloy has a hardness, at 75% work hardening, equal to at least 223 points according to the HV5 measurement method, optionally equal to at least 224 points according to the HV5 measurement method, and/or has a hardness, with 75% work hardening, of maximum 242 points according to the HV5 measurement method, optionally of maximum 240 points according to the HV5 measurement method.

According to a further non-limiting aspect, the Gold alloy has a hardness, at 50% work hardening, equal to at least 194 points according to the HV5 measurement method, optionally equal to at least 197 points according to the HV5 measurement method, and/or has a hardness, with 50% work hardening, of maximum 218 points according to the HV5 measurement method, optionally of maximum 215 points according to the HV5 measurement method.

According to a further non-limiting aspect, undergoing an environment containing Thioacetamide, particularly in an environment containing Thioacetamide according to the UNI EN ISO 4538:1998 standard, the alloy exhibits a color change DE (L* a* b*) within 24 h lower than 2.5, more preferably lower than 2.3 and even more preferably lower than 2.2.

According to a further non-limiting aspect, when immersed in 50g/liter aqueous solution of Sodium Chloride (NaCI) at 35°C for 24 h, the Gold alloy exhibits a color change DE (L*, a*, b*) lower than 2, more preferably lower than 1.9 and even more preferably lower than 1.8.

According to a further non-limiting aspect, said alloy is a homogeneous Gold alloy, free from second phases, and in particular free from carbides and/or oxides. According to the present disclosure, as "free of secondary phases" or "free of second phases" is intended an alloy free of elements that can generate said second phases, in particular in a melting process and subsequent solidification without further heating treatment; the second phases that are created in the liquid phase and remain after the solidification of the alloy, are harmful second phases, for example carbides and/or oxides that during the polishing are visible to the naked eye on the surface of the polished piece, and that therefore prevent to obtain objects of high surface quality, compatible with the requirements of high jewellery. It is possible to expose the alloy to heat treatment processes, suitable for giving it a hardening, such as due to precipitation can be present subtle precipitates, results of said heating treatment; in this case, these precipitates prevent the movement of the displacements, increasing the mechanical properties in the material, and contrast the onset of deformations in objects made with the present alloys.

According to a further non-limiting aspect, said alloy is a Gold alloy free from chemical elements likely to cause the generation of carbides and / or oxides.

According to a further non-limiting aspect, the Gold alloy is characterized by the absence of - or equivalently is free from - all metals belonging to the following list: Vanadium, Magnesium, Indium, Silicon, Tin, Titanium, Tungsten, Molybdenum, Niobium, Tantalum, Zirconium, Yttrium, Rhenium, Germanium. According to a further non-limiting aspect, the Gold alloy is a crystalline alloy, optionally 100% crystalline.

According to a further non-limiting aspect, said alloy is free from Nickel, Cobalt, Arsenic and Cadmium.

Also forming the subject matter of the disclosure is a method of producing a tarnishing resistant Gold alloy for jewellery, said method being characterized in that it comprises: a) a step of mixing and/or homogenization wherein all the pure elements constituting the alloy, according to one or more of the present aspects, are melted so as to obtain a homogeneous mixture; b) a step of introduction of the mixture into a melting pot, and of a subsequent melting by heating until melting.

According to a further non-limiting aspect, said melting is a continuous or discontinuous melting, comprising a casting step in which the melted material is cast into a die made of graphite or into a graphite bracket, and in which said mixture is a mixture of materials with properties chemically unrelated to graphite surfaces.

According to a further non-limiting aspect, said melting is a continuous melting, wherein the melted material is cast into a die made of graphite and wherein said mixture is a mixture of materials with anti-gripping properties on graphite surfaces, in particular at least free from Vanadium.

According to a further non-limiting aspect, after the continuous or discontinuous melting, said alloy is subjected to a cooling step followed by one or more hot or cold plastic deformation steps and one or more heating treatments.

According to a further non-limiting aspect, during said melting, the melting pot is subjected to a controlled gas atmosphere and in particular is subjected, at least temporarily, to a vacuum condition.

According to a further non-limiting aspect, during said continuous casting phase, said pot is subjected to a controlled atmosphere, at a pressure equal to or lower than the environmental pressure, and said gas is an inert gas, preferably argon, or a reducing gas, preferably forming gas.

According to a further non-limiting aspect, in said discontinuous casting step said pot is subjected to a controlled atmosphere lower than 800mbar, preferably lower than 700mbar, and said gas is an inert gas, preferably argon. It also forms the subject matter of the present disclosure an object of jewellery, comprising a Gold alloy according to one or more of the preceding aspects.

According to a further non-limiting aspect, said object of jewellery comprises a jewel or a watch or a watch bracelet or a movement or part of a mechanical movement for a watch.

According to a further non-limiting aspect, said watch or mechanical movement for a watch are configured to be worn or installed in wristwatches, respectively.

BRIEF DESCRIPTION OF DRAWINGS

The description of the present invention will be made with respect to some possible embodiments of Gold alloy wherein:

- Figure 1 shows a table including compositions of specific Gold alloy embodiments according to the present disclosure, expressed in thousandths by weight,

- Figure 2 shows a table comprising alloy hardnesses according to the FIV5 measurement method;

- Figure 3 shows a table comprising some embodiments of Gold alloys according to the present disclosure and shows the color coordinates of each of these embodiments and the color difference AE(L*,a*,b*), DE(I_*), AE(a*), AE(b*) with respect to the standard 5N color alloy;

- Figure 4 shows a table comprising some embodiments of Gold alloys according to the present disclosure and shows color variation data and also shows performance improvement factors of said embodiments;

- Figure 5 shows a chart representing a* and b* color coordinates for some embodiments of Gold alloy, and further shows tolerance limits for 5N color as understood by the ISO DIS 8564:2017 standard;

- Figure 6 shows a graph representing a combined enhancement factor for some embodiments of alloys according to the present disclosure, in relation to the color difference that these embodiments possess at instant t=0 with respect to the standard 5N alloy.

The invention is not limited to the embodiments shown in the appended figures. Therefore, it should be understood that where features or parts of the subject of the present disclosure are identified by signs, particularly numbers, for reference, such signs are included solely for the purpose of increasing the intelligibility of the description and claims, and are not intended in any way to be limiting.

DETAILED DESCRIPTION

The Applicant has conceived a family of jewellery alloys whose Gold content is substantially comprised between 19.55kt and 20.3kt; the alloys forming the subject of the present disclosure are of quinary type, and in particular essentially comprise Gold, Copper, Silver, Palladium and Platinum, and are tarnishing resistant.

Further alloys forming the subject of the present disclosure are alloys which essentially comprise Gold, Copper, Silver, Palladium and Platinum, and in addition an amount of Iridium and/or Ruthenium and/or Rhenium not higher than 2%o by weight and more preferably not higher than 1 %o by weight.

Gold alloys according to the present disclosure exhibit a color that is compatible with the color standard according to the ISO DIS 8564:2017 standard for 5N alloys.

Surprisingly, the Applicant has realized that combinations of Palladium and Platinum, especially for Gold contents substantially comprised between 19.55kt and 20.3kt (thus indicatively between 815 %o by weight and 846 %o by weight), in quinary alloys with Copper and Silver, in which Platinum does not exceed 1 0%o by weight, and in particular 7%o present color compatible with the 5N standard according to the ISO DIS 8654: 2017 standard, and a resistance to tarnishing significantly higher than both that of the standard 5N alloy and that of Copper- Silver quinary alloys with Gold contents at a title substantially equal to 791 %o and containing Platinum and Palladium in amounts equal to 5%o and 5%o, such as the LRS494 alloy mentioned in the PCT/IB2019/052092 document.

A first series of tests performed by the Applicant concerns quinary Gold alloys, with the following mixture:

- Gold in the amount comprised in the range [815-846] %o by weight,

- Copper in the amount comprised in the range [120-154] %o by weight,

- Silver in the amount comprised in the range [18-35] %o by weight,

- Platinum in the amount comprised in the range [1-10] %o by weight, - Palladium in the amount comprised in the range [7-15] %o by weight,

These tests, and also the tests performed on the subfamilies of Gold alloys described below, have been carried out both on pure quinary alloys, i.e. , in which the amount by weight of Gold, Copper, Silver, Platinum and Palladium is equal to 1 000%o, and non-quinary alloys comprising an amount not higher than 2%o and more preferably not higher than 1 %o of Iridium and/or Ruthenium and/or Rhenium.

The Gold alloys thus composed present, under the conditions of ISO DIS 8654:2017 standard, a color compatible with the color standard of 5N alloys.

A large part of the studies carried out by the Applicant have been focused on Gold alloys in which the ratio of the amounts by weight between Platinum and Palladium is substantially comprised between ½ (0.5), in particular 9/20 and more preferably 4/10, and ¼ (0.25).

A further series of tests involved Gold alloys in a narrower range of Copper contents; these quinary alloys comprise the following mixture:

- Gold in the amount comprised in the range [815-846] %o by weight,

- Copper in the amount comprised in the range [125-137] %o by weight,

- Silver in the amount comprised in the range [18-35] %o by weight,

- Platinum in the amount comprised in the range [1-10] %o by weight,

- Palladium in the amount comprised in the range [7-15] %o by weight,

Subsequently, the Applicant studied a plurality of quinary Gold alloys, in a narrower range of Gold than the preceding ones, and comprising:

- Gold in the amount comprised in the range [815-840] %o by weight,

- Copper in the amount comprised in the range [125-137] %o by weight,

- Silver in the amount comprised in the range [18-35] %o by weight,

- Platinum in the amount comprised in the range [1-7] %o by weight,

- Palladium in the amount comprised in the range [7-15] %o by weight.

The Applicant then focused on analysing the behaviour of Gold alloys that, compared to the previous ones, are enclosed in a more limited Silver amount range; these quinary alloys comprise:

- Gold in the amount comprised in the range [815-840] %o by weight,

- Copper in the amount comprised in the range [125-137] %o by weight,

- Silver in the amount comprised in the range [20-34] %o by weight,

- Platinum in the amount comprised in the range [1-7] %o by weight,

- Palladium in the amount comprised in the range [7-15] %o by weight. Further studies of the Applicant have focused on analysing two main subfamilies of Gold alloys, aimed at directing the study more and more selective on alloys comprising or Gold in the amount equal to 820 %o by weight or in the amount equal to 833 %o by weight. A first subfamily is the one in which Gold and Copper are present in the following ranges: Gold in the amount comprised in the range [827-839] %o by weight, and Copper in the amount comprised in the range [127-132] %o by weight.

Therefore, this first subfamily of Gold alloys is a subfamily of quinary alloys comprising:

- Gold in the amount comprised in the range [827-839] %o by weight,

- Copper in the amount comprised in the range [127-132] %o by weight,

- Silver in the amount comprised in the range [20-34] %o by weight,

- Platinum in the amount comprised in the range [1-7] %o by weight,

- Palladium in the amount comprised in the range [7-15] %o by weight.

Of this first subfamily, it has been particularly analysed a particular sector with narrower ranges of Gold, reaching the study of quinary Gold alloys comprising:

- Gold in the amount comprised in the range [830-836] %o by weight,

- Copper in the amount comprised in the range [127-132] %o by weight,

- Silver in the amount comprised in the range [20-34] %o by weight,

- Platinum in the amount comprised in the range [1-7] %o by weight,

- Palladium in the amount comprised in the range [7-15] %o by weight.

Subsequent studies were aimed at analysing the behaviour of quinary Gold alloys with ranges of Platinum and Palladium narrower than the previous ones, in particular quinary Gold alloys comprising: Platinum in the amount comprised in the range [1-6] %o by weight, and Palladium in the amount comprised in the range [8-13] %o by weight. The Applicant then has proceeded to perform further studies on Gold alloys by conceiving a family of quinary Gold alloys comprising:

- Gold in the amount comprised in the range [815-840] %o by weight,

- Copper in the amount comprised in the range [127-137] %o by weight,

- Silver in the amount comprised in the range [20-34] %o by weight,

- Platinum in the amount comprised in the range [1-6] %o by weight,

- Palladium in the amount comprised in the range [8-13] %o by weight. This family has been the subject of further studies and analyses, focusing on smaller values of Platinum and Palladium; a particular family of quinary Gold alloys has been conceived comprising:

- Gold in the amount comprised in the range [815-840] %o by weight,

- Copper in the amount comprised in the range [127-137] %o by weight,

- Silver in the amount comprised in the range [20-34] %o by weight,

- Platinum in the amount comprised in the range [1-5] %o by weight,

- Palladium in the amount comprised in the range [9-12] %o by weight.

A particular family of quinary Gold alloys belongs to the first subfamily previously mentioned, from which the specific example LRS 543 cited in the Table 1 below was later derived; this family of quinary Gold alloys comprises:

- Gold in the amount comprised in the range [827-839] %o by weight,

- Copper in the amount comprised in the range [127-132] %o by weight,

- Silver in the amount comprised in the range [20-34] %o by weight,

- Platinum in the amount comprised in the range [1-5] %o by weight,

- Palladium in amounts in the range [9-12] %o by weight.

Subsequent studies have focused on analysing the behaviour of the alloys of the family above described with even narrower ranges of Gold, thus conceiving a family of quinary Gold alloys comprising:

- Gold in the amount comprised in the range [830-836] %o by weight,

- Copper in the amount comprised in the range [127-132] %o by weight,

- Silver in the amount comprised in the range [20-34] %o by weight,

- Platinum in the amount comprised in the range [1-5] %o by weight,

- Palladium in the amount comprised in the range [9-12] %o by weight.

The second subfamily that then led to the conception of the specific embodiments LRS 544 and LRS545 is a family of Gold alloys centered around the specific Gold content at 820 %o by weight, and is therefore a second subfamily of quinary Gold alloys comprising: Gold in the amount comprised in the range [815-825] %o by weight, in combination with Copper in the amount comprised in the range [129-137] %o by weight.

The second subfamily of quinary Gold alloys therefore comprises:

- Gold in the amount comprised in the range [815-825] %o by weight,

- Copper in the amount comprised in the range [129-137] %o by weight,

- Silver in the amount comprised in the range [30-34] %o by weight, - Platinum in the amount comprised in the range [2-5] %o by weight,

- Palladium in the amount comprised in the range [8-13] %o by weight.

More particularly, this second subfamily comprises:

- Gold in the amount comprised in the range [815-825] %o by weight,

- Copper in the amount comprised in the range [129-137] %o by weight,

- Silver in the amount comprised in the range [31-33] %o by weight,

- Platinum in the amount comprised in the range [2-5] %o by weight,

- Palladium in the amount comprised in the range [8-13] %o by weight.

Even more particularly, this second subfamily comprises:

- Gold in the amount comprised in the range [815-825] %o by weight,

- Copper in the amount comprised in the range [132-136] %o by weight,

- Silver in the amount comprised in the range [31-33] %o by weight,

- Platinum in the amount comprised in the range [3-4] %o by weight,

- Palladium in the amount comprised in the range [10-11] %o by weight.

Returning to the first subfamily of Gold alloys, the Applicant's studies have focused toward the analysis of quinary Gold alloys with Gold in the amount comprised in a narrow range around 833 %o by weight, which comprise:

- Gold in the amount comprised in the range [832-834] %o by weight,

- Silver in the amount comprised in the range [22-24] %o by weight,

- Copper in the amount comprised in the range [129-131] %o by weight,

- Platinum in the amount comprised in the range [2-4] %o by weight,

- Palladium in the amount comprised in the range [10-12] %o by weight.

From these studies, the LRS 543 alloy in particular was derived, which is substantially a 20kt alloy (20kt would ideally correspond to 833.3 periodic %o by weight of Gold).

The specific embodiments LRS544 and LRS 545 are part of a particular subfamily belonging to said second subfamily of quinary Gold alloys, comprising:

- Gold in the amount comprised in the range [819-821] %o by weight,

- Silver in the amount comprised in the range [31-33] %o by weight,

- Copper in the amount comprised in the range [133-135] %o by weight,

- Platinum in the amount comprised in the range [3-5] %o by weight,

- Palladium in the amount comprised in the range [9-11] %o by weight.

In particular, this subfamily has led to a study aimed at the following alloys:

- Gold in the amount comprised in the range [819-821] %o by weight, - Silver in the amount comprised in the range [31-33] %o by weight,

- Copper in the amount comprised in the range [133-135] %o by weight,

- Platinum in the amount comprised in the range [2-4] %o by weight,

- Palladium in the amount comprised in the range [10-12] %o by weight. All the alloys herein described, undergoing an environment containing

Thioacetamide, in particular in an environment containing Thioacetamide according to the UNI EN ISO 4538:1998 standard, show a color variation DE (L* a* b*) within 24 h lower than 2.5, more preferably lower than 2.3 and even more preferably lower than 2.2. Some specific embodiments of Gold alloys conceived by the Applicant belong to the above-mentioned families and are shown in the following Table 1.

The alloys identified with code "ref" are not the subject of this disclosure, but are shown in the table for reference purposes.

Table 1 - alloy composition %o wt

It is noted that the specific embodiments LRS 543, LRS 544 and LRS 545 show an amount ratio by weight between Platinum and Palladium substantially comprised between ½, in particular 9/20 and more preferably 4/10, and ¼.

The Gold alloys according to the present disclosure have an initial hardness, without work hardening, equal to at least 125 points according to the HV5 measurement method, in particular equal to at least 128 points according to the HV5 measurement method. The Gold alloys according to the present disclosure have an initial hardness, without work hardening, of maximum 141 points according to the HV5 measurement method, in particular of maximum 139 points according to the HV5 measurement method.

The Applicant has carried out additional tests with 50% and 75% work hardening and obtained the following results. At 50% work hardening, the Gold alloys according to the present disclosure show a hardness equal to at least 194 points according to the HV5 measurement method, in particular equal to at least 197 points according to the HV5 measurement method; said alloys at 50% work hardening show a hardness of maximum 218 points according to the HV5 measurement method, in particular of maximum 215 points according to the HV5 measurement method.

At 75% work hardening, the Gold alloys according to the present disclosure show a hardness equal to at least 223 points according to the HV5 measurement method, in particular equal to at least 224 points according to the HV5 measurement method; said alloys at 75% work hardening show a hardness of maximum 242 points according to the HV5 measurement method, in particular of maximum 240 points according to the HV5 measurement method.

The Table 2 below shows hardness test results according to the HV5 measurement method for some specific embodiments of the Gold alloys that are the subject of the present disclosure. Alloys identified with code "ref" are not the subject of the present disclosure, but are shown in the table for reference.

Table 2 - alloy hardness according to the HV5 measurement method

It is noted that the alloys according to the present disclosure show a hardness substantially compatible with that of the standard 5N alloy, in particular resulting slightly less hard. Gold alloys with hardnesses in the above mentioned ranges, and particularly with the hardnesses shown in Table 2 are particularly suitable for watchmaking or high jewellery applications.

The Table 3 illustrates some embodiments of Gold alloys according to the present disclosure and shows the color coordinates of each of these embodiments and the color difference AE(L ^* ,a ^* ,b ^* ) (briefly referred to in the table as DE), DE(I_ ^* ) related to brightness only (briefly referred to in the table as DI_ ^* ), and AE(a ^* ), AE(b ^* ) (briefly referred to in the table as Aa ^* and Ab ^* ), related to chromaticity coordinates a* and b* with respect to the 5N standard color alloy. The alloys identified with code "ref" are not the subject of this disclosure, but are shown in the table for reference purposes.

Table 3 - color variations with respect to the 5N reference alloy (t = 0)

Although all of the alloys according to the present disclosure are compatible with the color standard for 5N alloys according to the ISO DIS 8564:2017 standard, it can be observed from the present table that the specific embodiments LRS543, LRS 544 and LRS 545, which have a Gold content equal to 833%o by weight, show a color that is closer to the color ideally proposed by the standard for the standard 5N alloy with respect to what is the case for the LRS 387 alloy of the known art, again with a Gold content equal to 833%o by weight: for this alloy, in fact, the color difference AE(L ^* a* b*) with respect to the standard 5N alloy is equal to 1.52, while the LRS543, LRS 544 and LRS 545 alloys show lower differences, comprised in the range [0.78 - 1.48] Thus, the Applicant has succeeded in conceiving a plurality of embodiments of alloys that with Gold in the amount equal to 833%o by weight, with Copper, Silver, Platinum and Palladium, shows tarnishing resistance and shows a color more similar to the standard 5N alloy with respect to the color assumed by the LRS 387 alloy of the known art. The Table 4 illustrates, in the first column, the color variations AE(L*,a*,b*) in Thioacetamide according to the UNI EN ISO 4538:1998 standard for some specific embodiments of Gold alloys. In the third column, this table illustrates color variations AE(L*,a*,b*) in NaCI solution as previously described.

The first three rows of the table illustrate embodiments of Gold alloys that are not part of the present disclosure. The column labeled "ref in previous tables for embodiments not part of the present disclosure has been omitted for compactness of the table.

The table also illustrates improvement factors which are described below. According to the present disclosure, the enhancement factor FM ^* (TIO) means the ratio between the color change AE(L ^* ,a ^* ,b ^* ) in Thioacetamide according to the reference standard for the 5N alloy and the color change AE(L ^* ,a ^* ,b ^* ) in Thioacetamide according to the reference standard for the alloy under consideration (all), at a given instant of time with respect to time zero (t = 0). In equations:

According to the present disclosure, FM ^* (NaCI) enhancement factor means the ratio between the color change DE(I_ ^* a ^* b ^* ) in Sodium Chloride according to the reference standard for the 5N alloy and the color change AE(L ^* ,a ^* b ^* ) in Sodium Chloride according to the reference standard for the alloy under consideration (all), at a given instant of time (t) with respect to time zero (t = 0). In equations:

In particular, tests relating to the resistance in a chloride-containing environment are performed by immersing the Gold alloy in a 50g/liter of Sodium Chloride (NaCI) aqueous solution at 35°C for a predetermined time, e.g., 24 h or

200 h.

According to the present disclosure, the combined enhancement factor FMC ^* means the product of the enhancement factor FM ^* (NaCI) with the enhancement factor FM ^* (TIO).

The percentage enhancements expressed in Table 5 are calculated according to the following equation: 00 100 i.e. by performing a subtraction between the color change AE(L ^* ,a ^* ,b ^* ) undergone by the 5N standard alloy in Thioacetamide (TIO) or in sodium chloride (NaCI) according to the reference standard in 24h and the color change AE(L* a* b*) undergone by the test alloy (all) in Thioacetamide (TIO) or Sodium Chloride (NaCI) according to the reference standard in 24h, dividing the result by the color change AE(L* a* b*) undergone by the 5N standard alloy in Thioacetamide (TIO) or Sodium Chloride (NaCI) according to the reference standard in 24h and multiplying the result obtained by 100.

Table 4 - enhancement factors The alloys according to the present disclosure, in particular the embodiments belonging to the following family [Gold in the amount comprised in the range [815-840] %o by weight, Copper in the amount comprised in the range [125-137] %o by weight, Silver in the amount comprised in the range [20-34] %o by weight, Platinum in the amount comprised in the range [1-7] %o by weight, Palladium in the amount comprised in the range [7-15] %o by weight] and more in detail the specific embodiments codified with LRS 543, LRS 544 and LRS 545 show when immersed in an 50g/litre of Sodium Chloride (NaCI) aqueous solution at 35°C for 24 hours, a color variation DE (L* a* b*) lower than 2, preferably lower than 1.9 and even more preferably lower than 1.8. In view of the above, it is observed that the alloys according to the present disclosure, and in particular the specific embodiments of Gold alloy coded with LRS 543, LRS 544, LRS 545 show a better behaviour than the LRS 387 alloy with equal amount of Gold (833%o by weight): with respect to this alloy, it can thus be observed that the effect of Platinum in a specific amount comprised between 1%o and 10%o and, in particular, in a specific percentage relationship with Palladium wherein the amount of Platinum is substantially comprised between ½, in particular 9/20 and more preferably 4/10 and 1/4 of the amount of Palladium, surprisingly improves the performance of the alloy, particularly in Thioacetamide both with respect to alloys free from Platinum and with respect to the reference alloy LRS494 with Platinum and Palladium, where the ratio between Platinum and Palladium is substantially equal to 1 or, equivalently, when Platinum and Palladium are present in the alloy in substantially equal amounts. In percentage ratio, and in Thioacetamide, the alloys subject of the present disclosure show a behaviour that improves their performance between about 2% and more than 20% with respect to the LRS 387 alloy with equal amount of Gold (833%o by weight).

In particular, the Applicant has observed that alloys close to LRS 543, i.e. , quinary Gold alloys with Gold in the amount comprised in the range [832-834] %o by weight, Silver in the amount comprised in the range [22-24] %o by weight, Copper in the amount comprised in the range [129-131] %o by weight, Platinum in the amount comprised in the range [2-4] %o by weight, Palladium in the amount comprised in the range [10-12] %o by weight show a surprisingly optimal behaviour in Thioacetamide with respect not only to the known Gold alloys, but also with respect to the best of the Gold alloys that are however subject of the present disclosure: indeed, among the specific embodiments mentioned in the present disclosure, the LRS 545 alloy has the best enhancement factor in Thioacetamide just ahead of LRS 543, and yet the performance between these two alloys differs by about 9.5% in favour of LRS 543. The Applicant has therefore noticed that going from a Gold content of 820 %o by weight to 833 %o by weight, with the same content of Platinum and Palladium, and mainly altering the amount of Silver causes a significant enhancement of the behaviour in Thioacetamide, which is not so evident instead in Sodium Chloride (where the difference in optimization of tarnishing resistance is only about 2.6% in favour of LRS 543 with respect to LRS 545).

It is also observed that the alloys according to the present disclosure, and in particular the specific embodiments of gold alloy coded with LRS 543, LRS544, LRS 545 show a remarkable improved behaviour with respect to the standard 5N alloy even in Sodium Chloride, and their enhancement factor is substantially comprised between 1.40 and 1.55 at 24h of exposure, which translates into an average percentage improvement of about 50% with respect to the standard 5N alloy.

The actual goodness of the alloys according to the present disclosure in terms of generic tarnishing resistance in both Thioacetamide and Sodium Chloride solution can be observed from the overall FMC enhancement factor at 24h, which shows that the specific embodiments close to LRS543 show an overall enhancement factor higher than 3 with respect to the 5N alloy, in particular equal to 3.79.

All the alloys according to the disclosure are free from materials capable of generating carbides and/or oxides, and in particular free from Vanadium. This allows the alloys in question to maintain a particular quality when processed. In particular, the alloys according to the disclosure are free from Magnesium, Indium, Silicon, Tin, Titanium, Tungsten, Molybdenum, Niobium, Tantalum, Zirconium, Yttrium, Rhenium, Germanium. In particular, it has been observed that Silicon greatly dulls the color of the resulting alloy, so that even minimal additions of Silicon in an alloy according to the formulations herein described would render the resulting alloy with a color not compatible with the color tolerances of 5N alloys, in particular according to ISO DIS 8654: 2017 standard. In addition, Silicon causes the formation of inclusions, often of significant size, which are inconvenient if alloys are to be made for high quality jewellery items, such as those herein described.

The Applicant has further found that alloys containing Silicon show worsening in terms of resistance to tarnishing, and this phenomenon is easily observable even with very low Silicon contents, in the order of a few thousandths. All the alloys according to the present disclosure are also expressly free from Nickel, Cobalt, Arsenic and Cadmium. This makes them suitable for use in making jewellery or parts of jewellery pieces in contact with the skin.

All the alloys according to the present disclosure are iron-free alloys; this allows to optimize the behaviour of the alloy in solutions containing NaCI, since Iron deteriorates its behaviour, worsening the resistance to tarnishing per time unit in NaCI solutions when the elements constituting the alloy and the percentages of them are those object of the present disclosure.

Subject to the exclusion of unwanted impurities, the alloys according to the disclosure may comprise additional metals in an overall amount, i.e. , in sum, not higher than 2%o and more preferably not higher than 1 % _<> ; the list of said additional materials comprises Iridium, Ruthenium and Rhenium. These materials can show, under determined conditions better explained later, grain refining properties. Finally, this list also comprises Zinc, as an element capable of reducing the content of dissolved oxygen in the alloy during the melting process.

In particular, Iridium is preferably used in alloys containing high Copper contents, as it has a wide miscibility range with the latter element; preferably, but not limited thereto, if present, Iridium is present in the amount equal to or lower than 0.3%o by weight. Rarer is the use of Ruthenium and Rhenium, in amounts up to 0.1 %o by weight. Ruthenium and Rhenium are preferably used in white or grey Gold alloys that contain high levels of Palladium.

However, it is pointed out that the use of Iridium, Rhenium and/or Ruthenium is subject to the inclusion of these elements in pre-alloys. In fact, it has been observed that these elements, if not pre-alloyed with their related material, but directly introduced into the pot, do not form an alloy, thus contributing to a worsening of the alloy characteristics. On the contrary, only if used in pre-alloy with Copper (Iridium) or Palladium (Rhenium and Ruthenium), taking care to alloy the pre-alloy with the rest of the elements composing the alloy itself, the grain refinement property is obtained.

The alloys according to the present disclosure are homogeneous Gold alloys, free from second phases, and in particular free from carbides and/or oxides, and/or are crystalline alloys, in particular 100% crystalline. This allows to have a high strength and surface quality and uniformity. “Free from secondary phases” or “free from second phases” mean an alloy free from elements capable of causing their occurrence, particularly in a melting process and subsequent solidification without further heating treatment; the second phases that are created in the liquid phase and remain after the solidification of the alloy, are harmful second phases, for example carbides and/or oxides that during the polishing phase are visible to the naked eye on the surface of the polished piece, and that therefore prevent from obtaining objects of high surface quality, compatible with the needs required in the field of high jewellery/watchmaking.

Production process It is also subject of the present disclosure a production process of a Gold alloy whose mixture is according to the present description.

The Gold alloys that are object of the disclosure are made from pure elements, in particular 99.99% Gold, 99.99% Cu, 99.95% Pd, 99.99% Fe, 99.99% Ag, 99.95% Pt.

The melting process of pure elements for creating Gold alloys according to the disclosure may be in detail a discontinuous Gold melting process or a continuous Gold melting process. The discontinuous Gold melting process is a process in which the mixture is melted and cast into a mould or ingot, made of graphite. In this case, the above indicated elements are melted and cast in a controlled atmosphere. More particularly, the melting operations are carried out only after preferably conducting at least 3 cycles of conditioning of the atmosphere of the melting chamber. This conditioning provides first of all for the achievement of a vacuum level up to pressures lower than 1x1 O ² mbar and a subsequent partial saturation with Argon at 500mbar. During the melting, the Argon pressure is kept at pressure levels comprised between 500mbar and 800mbar. When the complete melting of the pure elements has been achieved, a superheating phase of the mixture occurs, in which the mixture is heated up to a temperature of about 1250°C, and in any case at a temperature above 1200°C, in order to homogenize the chemical composition of the metal bath. During the superheating phase, the pressure value in the melting chamber reaches again a vacuum level lower than 1x1 O ² mbar.

At this point, in a casting step, the melted material is poured into a mould or ingot, and the melting chamber is again pressurized with an inert gas, preferably argon, injected at a pressure lower than 800mbar and particularly lower than 700mbar.

When solidified, bars or castings are extracted from the bracket. After solidification of the alloy, bars or castings of Gold alloy are obtained which are subject to a rapid cooling by immersion in water in order to reduce and possibly avoid phase transformations in the solid state. In other words, the bars or castings are subject to a rapid cooling step, preferably but not limiting in water, in order to avoid phase changes in the solid state. The continuous melting process is a process in which the solidification and the extraction of solidified Gold are continuously performed from a free end of a Gold bar or casting. In particular, a graphite die is used in the continuous melting process. The use of graphite dies is well known, since graphite is a solid lubricant, and has typically low friction between its surfaces and those of the solidified metal, typically allowing for an easy extraction of the element contained therein without fractures and with the least quantity of defects present on its surface.

In the mixing step above described, the pure base elements are mixed in such a way as to obtain a homogeneous mixture, i.e., free from portions or areas characterized, particularly significantly, by a surplus of one element with respect to the others.

When the inclusion of elements such as Iridium, Ruthenium and Rhenium by grain refinement is present, the production process comprises a step of producing a pre-alloy, wherein said pre-alloy comprises: (a) Iridium pre-alloyed with Copper in the amounts already indicated, or alternatively. b) Rhenium or Ruthenium pre-alloyed with Palladium in the amounts already indicated.

Subsequently, the bars or castings obtained by discontinuous or continuous melting are subject to a hot or cold plastic deformation step, preferably but not limiting to flat rolling.

During the flat rolling and more generally during the cold plastic processing stages, the different melted compositions according to the previously described procedure are deformed over 60% and then subject to a recrystallization heating treatment at a temperature higher than 650°C, to be subsequently cooled.

In the production process of the Gold alloy herein described, it is anyway possible to subject the alloy to heating treatment processes, suitable for giving it a hardening, so that by precipitation may become present thin precipitates, results of said heating treatment; in this case they are precipitates that prevent the movement of dislocations increasing the mechanical properties in the material, and contrast the onset of deformations in objects made with the present alloys.

Finally, it is object of the disclosure a jewellery piece comprising a Gold alloy according to the characteristics previously described. Although said piece of jewellery can assume the most varied forms and characteristics, in particular it comprises a jewel, for example and not limiting to a bracelet, also with bezels, a necklace, earrings, rings, or a watch or a bracelet for a watch or a movement or part of a mechanical movement for a watch. In particular, said watch or mechanical watch movement are configured to be worn or installed in wristwatches, respectively. With the use of the Gold alloys object of the disclosure said jewellery pieces show a color, defined as "red" according to 5N standard, sufficiently stable even for use in particularly aggressive conditions, such as for example in contact with the skin in case of heavy perspiration or in a marine environment (the latter being an environment where typically wedding rings and/or underwater watches with portions of e.g. Gold bracelet or case are typically however worn by the user); these jewellery pieces, in this way, are also characterized by the absence of components susceptible to cause allergies, and are also provided with sufficient hardness. Finally, it is clear that modifications, additions or variations to the object of the present disclosure may be applicable, which are obvious to a person skilled in the art, without exceeding the scope provided by the appended claims.