Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C9/00—Alloys based on copper
• • A—HUMAN NECESSITIES
  • A44—HABERDASHERY; JEWELLERY
  • A44C—PERSONAL ADORNMENTS, e.g. JEWELLERY; COINS
  • A44C27/00—Making jewellery or other personal adornments
  • A44C27/001—Materials for manufacturing jewellery
  • A44C27/002—Metallic materials
  • A44C27/003—Metallic alloys
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C1/00—Making non-ferrous alloys
  • C22C1/02—Making non-ferrous alloys by melting
• • G04B37/221—
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
  • C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
  • C22F1/08—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of copper or alloys based thereon

Definitions

• the present invention refers to the field of Gold alloys and in particular refers to a Gold alloy with Gold title substantially equal to 9 carats (9K).
• the present invention also refers to a method for the production of a Gold alloy.
• the Gold alloy and the method for the production of Gold alloys according to the invention are an alloy and a method for the production of Gold alloys for jewellery and watchmaking applications respectively.
• Gold is not used in pure form, since it is too ductile.
• Gold alloys for jewellery or watchmaking characterized by a higher hardness with respect to the Gold in pure form and/or with respect to low hardness or high ductility Gold alloys.
• Colors for Gold alloys can be uniquely measured in the CIELAB 1976 color space, which defines a color on the basis of a first L* parameter, a second a* parameter and a third b* parameter, wherein the first L* parameter identifies the brightness and adopts values comprised between 0 (black) and 100 (white) whereas the second a* parameter and the third b* parameter represent chromaticity parameters.
• the Cab* parameter is defined as“chroma”; the higher the value of Cab* parameter is, the higher is the color saturation; the lower the value of Cab* parameter is, the lower is the color saturation, that will tend to the grey scale.
• alloys with a Gold content higher than 750%o which can be used as such as white or grey Gold alloys and do not require surface rhodium plating, arbitrarily show Cab* values ⁇ 8.
• the parameter h abt identifies on the other hand the tonality of the color.
• the ISO DIS 8654:2017 standard defines seven color designations as for the Gold alloys for jewellery.
• these alloys are defined according to the following table, wherein the color is defined on a standard reference specified between ON and 6N.
• the ISO DIS 8654 standard specifies that the measuring instrument must comply with the CIE N° 15 publication.
• the ISO DIS 8654:2017 standard also shows the nominal values L* a* b* as trichromatic coordinates for alloys of 0N-6N standard color, including the tolerances.
• L* a* b* as trichromatic coordinates for alloys of 0N-6N standard color, including the tolerances.
• an abstract of the standard wherein are defined the chromatic limits of the alloys defined by the ISO DIS 8654:2017 standard as pink/red.
• the ISO DIS 8654:2017 standard also proposes chemical compositions recommended for each of the 0N-6N alloys.
• the compositions are the ones specified in the table:
• the pink/red Gold alloys of known type show a substantial color instability, in particular when exposed to environments wherein there are chlorides or sulphides.
• the Applicant has noted that the 5N ISO DIS 8654:2017 Gold alloy in the formulation that uses the minimum reference value as for the content of Silver exposed to vapors of thioacetamide for 150 hours (according to the UNI EN ISO 4538:1998 standard), shows a variation of color DE (L* a* b*) equal to 5.6; when exposed to the action of an aqueous solution 50g/liter of sodium chloride (NaCI) at 35°C for 175 hours, the 5N Gold alloy shows a variation of color DE (L* a* b*) equal to 3.6.
• jewellery alloys comprising Gold with a title equal to or substantially equal to 9K. These Gold alloys are typically used to make jewels of value lower than those made with 18K or higher Gold alloys.
• alloys including Gold with a title equal to or substantially equal to 9K there are known alloys containing Copper, suitable to appear with a pink or red color, according to a growing percentage of Copper in the alloy.
• the presence of Copper has the drawback of being rather prone to vary color especially when the object of jewelry is worn and exposed to human sweating and/or saline environment.
• the same alloys, including Gold with a title equal to or substantially equal to 9K are known to have significant color variation even just after exposure to air.
• the plating of a jewellery item with high title Gold alloys is expensive, and significantly contributes to the increase in the production cost of the item not only because of the cost of the high title Gold alloy, but also because of the further necessary processing on the jewellery item, which incidentally for shapes of jewellery items of considerable complexity, may not be insignificant.
• the plating representing the surface layer of the item, is the portion the most subject to wear or anyhow removal; with the removal of the plating, the item of jewelry may have exposed portions of alloy with Gold title equal to or substantially equal to 9K, which - exposed to chemically aggressive environments - may have different color than the portions that vice versa still carry the plating alloy.
• the purpose of the present invention is therefore to describe a Gold alloy, particularly for jewelry and watchmaking, with a Gold title equal to or substantially equal to 9K, which solves the above described drawbacks, in particular being not very prone to turn color when exposed to environments with air, Thioacetamide or NaCI in solution.
• the purpose of the present invention is also to describe a method of production of an alloy containing Gold with a title equal to or substantially equal to 9K, which solves the above described drawbacks.
• the purpose of the present invention is finally to describe an item of jewelry or part of an item for jewelry, made with the alloy object of the invention, which does not show the above described drawbacks.
• an alloy in particular for jewellery, characterized in that it comprises:
• Said alloy in particular consists of:
• Palladium in the amount comprised between 5%o and 35%o in weight and, optionally, at least one among: Iron in the amount comprised between 2%o in weight and 25%o in weight, Silver in the amount lower than or equal to 100%o in weight, Zinc in the amount lower than or equal to 100%o in weight, Indium in the amount lower than or equal to 20%o in weight, Tin in the amount lower than or equal to 20%o in weight, Gallium in the amount lower than or equal to 10%o in weight, Iridium in the amount lower than or equal to 0.5%o in weight, or Ruthenium in the amount lower than or equal to 0.5%o in weight, Rhenium in the amount lower than or equal to 0.1 %o in weight.
• the sum of Palladium and Iron is equal to 30%o in weight.
• as“jewellery alloy” is intended an alloy, in particular a Gold alloy, in which there are no materials toxic to humans and the formulation of which is suitable for, specifically designed for, making jewels, or parts thereof.
• the alloy according to the first aspect is a Gold alloy characterized by a dark red color.
• as“dark red” is intended a color that, arbitrarily, on the a*, b* color plan according to the CIE 1976 color chart, is not comprised in the spaces defined by the ISO DIS 8654:2017 standard and is enclosed in a polygon at least defined by the following points:
• the alloy according to a first or second aspect is a tarnishing resistant alloy.
• the alloy depending on one or more of the preceding aspects, comprises Palladium in the amount comprised between 8%o, more preferably 10%o in weight, and 32%o, more preferably 30%o in weight.
• the alloy according to one or more of the preceding aspects comprises also Iron in the amount comprised between 2%o in weight and 25%o in weight, more preferably comprised between 5%o in weight and 20%o in weight.
• the alloy according to one or more of the preceding aspects is a ternary or quaternary alloy, and the sum of the amounts of Gold, Copper and Palladium is at least equal to 900%o in weight.
• ternary or quaternary Gold alloy an alloy wherein there are 3 or 4 components respectively, the amount of which is not negligible, and in particular higher than 2%o in weight and more preferably higher than 1 %o in weight.
• quaternary or quinary alloys do not comprise components in excess of 2%o in weight and more preferably 1 %o in weight in addition to those explicitly mentioned.
• the alloy according to the 6° aspect shows a sum of the amounts of Gold, Copper and Palladium at least equal to 960%o in weight, more preferably 970%o in weight.
• the alloy according to the 6° aspect comprises also Silver in the amount lower than 100%o in weight, and/or Zinc in the amount lower than 100%o in weight or Silver and Zinc the sum of respective amounts in weight is lower than 100%o .
• the alloy according to one of the aspects from 1 ° to 7° comprises Palladium in the amount comprised between 15%o in weight and 25%o in weight, more preferably between 18%o in weight and 22%o in weight, more preferably substantially equal to 20%o in weight.
• the alloy according to one of the aspects from 1 ° to 7°, when depending on the 5° aspect, the sum of the amounts of Palladium and Iron is equal to 30%o in weight.
• the Gold is present in the amount comprised between 365%o in weight and 385%o in weight and Copper is present between 594%o in weight and 614%o in weight and Palladium is comprised between 15%o and 25%o in weight, more in particular between 18%o and 22%o in weight.
• the alloy subject of the invention is an alloy whose color on the CIELAB1976 color chart shows a coordinate a* > 8.2 and a coordinate b* ⁇ 13.5.
• said Gold alloy for jewellery is an alloy characterized by the absence of Vanadium, and other materials capable to create carbides and oxides, in particular free from Magnesium, Silicon, Titanium, Tungsten, Molybdenum, Niobium, Tantalum, Zirconium, Yttrium, Germanium.
• the Gold alloy for jewellery is an alloy free from Nickel, Cobalt, Arsenic and Cadmium. Thanks to this aspect, the alloy is a Gold alloy compatible with being worn or wearable by subjects whose allergic tolerance is significantly low.
• - Gold in the amount comprised between 330%o and 420%o in weight
• - Copper in the amount comprised between 500%o and 620%o in weight
• - Palladium in the amount comprised between 5%o and 35%o in weight and, optionally, at least one among: Iron in the amount comprised between 2%o in weight and 25%o in weight, Silver in the amount lower than or equal to 100%o in weight, Zinc in the amount lower than or equal to 1 00%o in weight, Indium in the amount lower than or equal to 20%o in weight, Tin in the amount lower than or equal to 20%o in weight, Gallium in the amount lower than or equal to 10%o in weight, Iridium in the amount lower than or equal to 0.5%o in weight, or Ruthenium in the amount lower than or equal to 0.5%o in weight, Rhenium in the amount lower than or equal to 0.1 %o in weight.
• said step comprises mixing in particular Palladium in the amount comprised between 8%o, more preferably 10%o, and 32%o, more preferably 30%o in weight.
• the alloy according to one or more of the preceding 16°-17° aspects comprises in particular mixing, in addition to the preceding elements, also Iron in the amount comprised between 2%o in weight and 25%o in weight, more preferably comprised between 5%o in weight and 20%o in weight.
• the sum of the amounts of Gold, Copper and Palladium is at least equal to 900%o in weight.
• the step comprises the mixing of Gold,
• the alloy according to the 19° aspect comprises the mixing of Silver in the amount lower than 100%o in weight, and/or Zinc in the amount lower than 100%o in weight or Silver and Zinc the sum of respective amounts in weight is lower than 100%o.
• said step comprises the mixing of Palladium in the amount comprised between 15%o in weight and 25%o in weight, more preferably between 18%o in weight and 22%o in weight, more preferably substantially equal to 20%o in weight.
• the sum of the amounts of Palladium and Iron is equal to 30%o in weight.
• the Gold is mixed in particular in the amount comprised between 365%o in weight and 385%o in weight and Copper is present between 594%o in weight and 614%o in weight and Palladium is comprised between 15%o and 25%o in weight, more preferably between 18%o and 22%o in weight.
• said homogenization is a discontinuous melting, comprising a step of casting wherein the melted material is casted in a refractory mold or refractory or metallic ingot and wherein said melted alloy is an alloy characterized by the absence of Vanadium, and other elements capable to create carbides or oxides, in particular free from Magnesium, Silicon, Titanium, Tungsten, Molybdenum, Niobium, Tantalum, Zirconium, Yttrium, Germanium.
• the absence of said carbides or oxides makes the Gold alloy suitable for applications of jewelry and watchmaking where polishing or diamond polishing of finished items is required.
• the melting pot is subject to a gas controlled atmosphere and in particular is subject, at least temporarily, to vacuum condition.
• said melting pot is subject to a controlled atmosphere, to pressures lower than the environmental one.
• said controlled atmosphere is or comprises an inert gas, preferably argon and/or said pressure is a pressure lower than 800mbar, preferably lower than 700mbar.
• said gas is a reducing gas, preferably a hydrogen-nitrogen mixture and/or said pressure is a pressure lower than 800m bar, preferably lower than 700mbar.
• said melting is a continuous melting, comprising a step of melting and homogenization in a graphite pot and a subsequent melting step wherein the melted alloy is casted in a die realized in graphite and wherein said alloy is an alloy of metals without chemical affinity to graphite and more specifically, in particular at least free from Vanadium, Magnesium, Silicon, Titanium, Tungsten, Molybdenum, Niobium, Tantalum, Zirconium, Yttrium, Germanium.
• said alloy is subject to a cooling step followed by one or more hot or cold plastic deformation steps and one or more thermal treatments.
• an item of jewellery comprising a Gold alloy according to one or more of the preceding aspects concerning said Gold alloy.
• said item of jewellery comprises a jewel or a watch or a watch bracelet or a movement or part of a mechanical movement for watches.
• said watch or mechanical movement for watches are configured for being respectively worn or installed in wristwatches.
• an alloy in particular for jewellery, characterized in that it comprises at least:
• the Gold alloy is free from secondary phases, and/or is a homogeneous alloy, and/or is a crystalline alloy, optionally 100% crystalline.
• as“free from secondary phases” or“free from second phases” is intended an alloy free from elements that can generate said second phases, in particular in a proceeding of melting and subsequent solidification without other thermal treatments; second phases that create in the liquid phase and remain downstream of the alloy solidification, are harmful second phases, for example carbides and/or oxides that during the polishing step are visible at naked eye on the surface of the polished item, and that then prevent to obtain items of high surface quality, compatible with the needs required in the high jewellery field.
• FIG. 1 shows a portion of CIELAB 1976 color space according to the coordinates L* a* b* wherein it has been detected an area corresponding to color intervals or tolerances admissible for Gold alloys according to the 5N and 6N ISO DIS 8654:2017 standard and wherein it is shown the typical color position for alloys object of the present invention
• FIG. 3 shows a color variation chart according to the time of exposure to Thioacetamide solutions according to UNI EN ISO 4538 for part of the alloys object of the present invention, in relation to the color variation gained by the
• FIG. 5 shows a curve of variation of the color variation rate of various alloys object of the present invention when exposed for a determined time period to NaCI aqueous solution according to the content of Palladium.
• the alloys that are described in the present invention have been tested in terms of resistance to color variation (tarnishing) in environments comprising Thioacetamide and NaCI solutions (sodium chloride).
• any reference to tests carried out in an environment comprising Thioacetamide is made according to the indications of the UNI EN IS04538: 1998 standard.
• the samples are exposed to vapours of Thioacetamide CH 3 CSNH 2 in an atmosphere with relative humidity of 75% kept through the presence of a saturated solution of sodium acetate trihydrate CFhCOONa-SFhO in a test chamber with a capacity comprised between 2 and 20 litres and wherein all the materials used for the construction of the chamber itself are resistant to volatile sulphides and do not emit any gas or vapour capable of influencing the results of the test.
• the tests have been carried out by immersing the samples of a Gold alloy in a 50g/L NaCI solution at neutral pH, thermostated at 35°C.
• the alloy object of the invention may consist of an alloy, in particular for jewellery, characterised by the fact that it consists of:
• with“tarnishing” is intended a surface corrosion of the Gold alloy that causes a variation in the alloy color.
• the family of Gold alloys object of the invention comprises at least ternary alloys, and more in particular ternary or quaternary alloys. Therefore, the number of elements that are included in a not insignificant amount in the family of Gold alloys object of the invention is at least equal to 3 and, preferably, not higher than 4, although quinary formulations may still be possible and include elements not included in the preceding table.
• the Applicant has carried out various experiments for assessing the resistance to tarnishing and the so obtained color of the alloys, and in particular has carried out experiments on the specific embodiments indicated in the following table:
• the alloys according to the preceding formulations are preferred and non- limiting examples of Gold alloy for jewellery with a title equal to or substantially equal to 9K.
• the tarnishing resistance tests carried out by the Applicant and reported below have been carried out with respect to a reference alloy, in particular a reference ternary alloy comprising Gold, Copper and Silver, whose composition is the following.
• the LRS 362 alloy used as reference test does not have a“dark red” color, but a significantly different color, which lies within the tolerances for alloys whose color is compatible with 6N ISO.
• the alloys according to the family generally described as the object of the invention and, consequently, the specific realizations described in table 5 are realizations characterized by the absence of Silver.
• Silver is known to be an element that in these alloys helps to increase the hardness.
• the 362 alloy used as reference test in the absence of work hardening, has a hardness according to HV5 equal to 139, which becomes equal to 185 with 25% work hardening, equal to 210 with 50% work hardening and equal to 245 with 75% work hardening.
• the following table shows the hardnesses obtained for the specific alloy formulations according to the present invention, as well as for the LRS 362 alloy used as reference test.
• the Applicant has observed that the specific formulations of Gold alloy described in table 7 have hardness, even under conditions of non-work hardening, compatible with that of alloys for jewellery in accordance with the present invention.
• the LRS 496 and LRS 498 formulations are respectively the closest to the behavior in terms of hardness possessed by the LRS362 alloy used as reference test (whose alignment in the table is offset for ease of identification), and even better (LRS 498) with respect to the alloy used as reference test.
• the Applicant has highlighted that in a 9K quaternary Gold-Copper-Palladium and Iron alloy, having a quantity substantially equal to 40%o of Palladium and Iron, and in particular having Palladium and Iron in amounts respectively comprised, each one, between 1 8%o and 22%o, and even more in particular each one in amounts equal to 20%o allows to obtain alloys whose hardness is substantially higher than the LRS362 reference alloy, at least up to a level of hardening equal to 50%.
• All the alloys according to the general formulation, and in particular all the specific realizations of the alloys according to table 5 have a better behaviour, both in NaCI solution and in Thioacetamide, with respect to the LRS362 alloy used as reference test.
• the alloy used as a reference test has a color that is not compatible with that of the alloys object of the invention, the latter have a significantly lower trend to change color.
• the Applicant has observed that the optimization of the alloy behavior in terms of tarnishing is optimized - in the ranges identified in the preceding family, for Palladium values comprised within the following range: [8%o - 32%o] in weight, and even more preferably for Palladium values within the range of [1 0%o - 30%o] in weight.
• the Applicant has surprisingly verified that the optimization of the resistance to tarnishing is obtained, for the family as generally above expressed, for Palladium contents in the amount comprised between 1 5%o in weight and 25%o in weight, more in particular between 1 8%o in weight and 22%o in weight, and in particular for Palladium contents substantially equal to 20%o in weight.
• the Applicant has observed a substantial optimal behavior of performances in NaCI, in particular when Iron content in the alloy is lower than 20%o and in particular when Iron content is lower than or equal to 10%o.
• alloys according to the LRS 496 and 497 formulation respectively with an Iron content equal to 10%o in weight and zero, have an optimized behavior.
• the Applicant was able to conceive alloys that, with the above mentioned formulations and in particular with Palladium comprised between 18%o and 22%o and Iron in the amount lower than or equal to 10%o, the performances of a 9K alloy are substantially close to that of an alloy according to the 5N ISO standard, which has a significantly higher Gold title, because at 18K. Therefore, it was almost possible to achieve, in terms of tarnishing, the behavior of an 18K alloy with an alloy whose Gold content is significantly lower, being 9K.
• the Applicant has observed that the alloy must be preferably ternary or quaternary, with the necessary presence of Palladium and with the sum of the amounts of Gold, Copper and Palladium at least equal to 900%o in weight.
• the remaining 100%o in weight can be of different materials, including Silver or Zinc or combinations of Silver or Zinc in order to vary at least the specific color of the alloy while remaining within the color previously defined as“dark red”.
• all the embodiments specifically identified in Table 5 are specific optimized embodiments taken from a subfamily of alloys in which the sum of the amounts of Gold, Copper and Palladium is at least equal to 960%o in weight and, even more preferably 970%o in weight; alloys with this last characteristic have a substantially assimilable behavior in the complex, observing the color variations in air, in Thioacetamide and in NaCI solution.
• alloys according to the invention can comprise additional materials in total 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, Indium and Rhenium. These materials can have, under certain conditions better explained hereinafter, grain refining properties.
• Iridium is preferably used in alloys containing high Copper contents, because it binds in particular with the latter element; preferably, but non- limiting thereto, if present, Iridium is present in an amount equal to or lower than 0.5%o in weight.
• Rarer is the use of Ruthenium and Rhenium, in a sometimes lower amount, but anyway up to 0.5 %o in weight.
• Ruthenium and Rhenium are used in Gold alloys containing Palladium or Zinc in the amount lower or equal to 100%o.
• the use of Iridium and/or Rhenium and/or Ruthenium is subject to the inclusion of these elements in pre-alloys.
• the Gold alloy for jewellery is preferably characterized by the absence of Vanadium and other materials capable to create carbides and oxides, in particular free from Magnesium, Silicon, Titanium, Tungsten, Molybdenum, Niobium, Tantalum, Zirconium, Yttrium, Germanium.
• This alloy is also an alloy free of Nickel, Cobalt, Arsenic and Cadmium. Thanks to this aspect, the alloy is a Gold alloy compatible with being worn or wearable by subjects whose allergic tolerance is significantly low.
• the Gold alloys object of the invention are made from pure elements, in particular from Gold at 99.99%, Cu at 99.99%, Pd at 99.95%, Fe at 99.99%.
• the process of melting of pure elements for the creation of the Gold alloys according to the invention can be in detail a process of discontinuous melting of Gold or a process of continuous melting of Gold.
• the process of discontinuous melting of Gold is a process in which the mixing is melted and cast into a refractory mold or refractory or metallic ingot mould. In this case the above mentioned elements are melted and cast in a controlled atmosphere. More in particular, the melting operations are carried out only after having preferably conducted at least 3 conditioning cycles of the atmosphere of the melting chamber. This conditioning involves first of all reaching 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 between 500mbar and 800mbar.
• a phase of overheating of the mixture takes place, in which the mixture is heated up to a temperature of about 1250°C, and in any case to a temperature above 1200°C, in order to homogenize the chemical composition of the metal bath.
• the pressure value in the melting chamber reaches again a vacuum level lower than 1x1 O 2 mbar, useful to eliminate part of the residues produced by the melting of the pure elements.
• the melted material is casted into a mould or ingot mould realized in graphite and the melting chamber is again pressurized with an inert gas, preferably argon, injected at a pressure lower than 800mbar and in particular lower than 700mbar.
• an inert gas preferably argon
• the bars or casts are extracted from the bracket.
• the alloy is solidified, from the mold in graphite are obtained Gold bars or Gold alloy casts which are subjected to quick cooling by means of a step of immersion in water, in order to reduce and possibly avoid solid state phase transformations.
• the bars or casts are subjected to a quick cooling phase, preferably but non- limiting in water, in order to avoid phase variations in the solid state.
• the production process of the Gold alloy according to the invention comprises, starting from the pure elements according to the above, a mixing step of elements according to the present disclosure, and in particular:
• the process of continuous melting is a process in which solidification and extraction of the solidified Gold are continuously carried out from one free end of a Gold bar or cast.
• a graphite die is used in the continuous melting process.
• the use of graphite dies is known, since graphite is a solid lubricant, and typically has low friction between its surfaces and those of the solidified metal, permitting to obtain an easy extraction of the element contained therein without fractures and with the minimum amount of defects present on its surface.
• Rhenium is present for grain refinement, the production process comprises a step of realizing of a pre-alloy, in which said pre-alloy comprises:
• the bars or casts obtained by discontinuous or continuous melting are subject to a step of cold plastic deformation, preferably but non-limiting to flat rolling.
• the different compositions synthesized according to the previously described melting procedure are deformed by more than 70% and then subjected to a thermal treatment of solubilization at a temperature higher than 680°C, in order to be subsequently cooled.
• Particular embodiments of the previously described method include an initial step in which are mixed in particular Palladium in the amount comprised between 8%o, more preferably 10%o, and 32%o, more preferably 30%o in weight and/or, in addition to the preceding elements, also Iron comprised between 2%o in weight and 25%o in weight, more preferably between 5%o in weight and 20%o in weight.
• the sum of the amounts of Gold, Copper and Palladium is at least equal to 900%o in weight, and more in particular in the amount at least equal to 960 %o in weight, more preferably 970 %o in weight.
• the Gold is mixed in particular in the amount comprised between 365%o in weight and 385%o in weight and Copper is present between 594%o in weight and 614%o in weight and Palladium is comprised between 15%o and 25%o in weight, more preferably between 18%o and 22%o in weight.
• the advantages offered by the alloy object of the invention are clear in the light of the above obtained description.
• the alloys are characterized by a low trend to tarnishing for the environments in which an item of jewellery is typically found to be used, consequently it allows to realize items of jewellery or parts of items for jewellery resistant to tarnishing, in substantially red color as above defined, without the need for subsequent plating with high title Gold alloys. Consequently, the item of jewellery thus created is less expensive and less demanding to be processed as well as characterized by a substantially more uniform color even after wear.
• the alloys according to the present disclosure are alloys without secondary phases.
• 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 permits to have a high strength and quality and surface uniformity.
• As“free from secondary phases” or“free from second phases” is intended an alloy free from elements that can generate them, in particular in a process of melting and subsequent solidification without other thermal treatments; second phases that create in the liquid phase and remain downstream of the alloy solidification, are harmful second phases, for example carbides and/or oxides that during the polishing step are visible at naked eye on the surface of the polished item, and that then prevent to obtain items with high surface quality, compatible with the needs required in the high jewellery field.

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