Patent ID: 12252769

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention concerns a gold alloy, called 18 carat red gold, comprising, in weight percent, the following elements:75% to 77.5% of gold;0.5% to 3% of palladium;10% to 18% of silver;5% to 13% of copper,
wherein the respective percentages of all the alloying elements add up to 100%, and said alloy contains neither zinc, nor germanium, nor nickel, nor cobalt, nor indium.

The present invention also concerns a timepiece, or piece of jewellery or gem jewellery made of such an alloy and the use of such an alloy to make a timepiece, or piece of jewellery or gem jewellery.

Advantageously, said gold alloy contains, in weight percent, between 75% and 77.5% of gold, between 0.5% and 3%, preferably between 0.5% and 2% of palladium, between 10% and 18% of silver, between 5.5% and 13%, preferably between 6.5% and 13% of copper, wherein the respective percentages of all the alloying elements add up to 100%.

Advantageously, said gold alloy contains, in weight percent, between 75% and 77.5% of gold, between 0.5% and 3% of palladium, between 11% and 17% of silver, preferably between 11.2% and 17% of silver, between 5% and 12% of copper, wherein the respective percentages of all the alloying elements add up to 100%.

Preferably, said gold alloy contains, in weight percent, between 75% and 77.5% of gold, between 0.5% and 3% of palladium, between 11.2% and 17%, preferably between 11.5% and 17% of silver, between 6% and 13%, preferably between 6% and 12% and more preferably between 6% and 11% of copper, wherein the respective percentages of all the alloying elements add up to 100%.

According to another preferred embodiment, the gold alloy contains, in weight percent, between 75% and 77.5% of gold, between 0.5% and 3% of palladium, between 12% and 16% of silver, between 6% and 10.5%, preferably between 6% and 10% of copper, wherein the respective percentages of all the alloying elements add up to 100%.

According to another preferred embodiment, the gold alloy contains, in weight percent, between 75% and 77.5% of gold, between 1% and 2.5% of palladium, between 12.5% and 15.5% of silver, between 6% and 9% of copper, wherein the respective percentages of all the alloying elements add up to 100%.

According to another preferred embodiment, the gold alloy contains, in weight percent, between 75% and 77.5% of gold, between 1% and 2.5%, preferably between 1% and 2% of palladium, between 13% and 15%, preferably between 14% and 15%, and more preferably between 14.5% and 15% of silver, between 7.5% and 9% of copper, wherein the respective percentages of all the alloying elements add up to 100%.

Preferably, the gold alloy contains 1.5 wt. % of palladium.

Preferably, in any of the embodiments described above, the gold alloy can also contain a maximum of 0.05 wt. % of any one element or a combination of elements chosen from the group including iridium, rhenium and ruthenium. Advantageously, the alloy can contain 0.0025 wt. % of iridium.

The gold alloys of the invention find particular application in the production of timepieces, or pieces of jewellery or gemstone jewellery, such as a watch case, a dial, a bracelet, a bracelet clasp, a jewel, an accessory, etc. In this application, the alloy makes it possible to obtain timepieces, pieces of jewellery or gemstone jewellery made of 18 carat yellow gold offering better resistance to discolouration and tarnishing.

This invention will now be illustrated in more detail by means of the following non-limiting examples.

EXAMPLES

Table 1 shows the composition of the alloy No. 1444 in wt. % % according to the invention and of the alloys No. 2N, No. 3N, No. 126, which are 18 carat gold alloys, of the prior art.

TABLE 1NoAuAgCuPdIr2N (comparative750.616089.4sample)3N (comparative750.6125124.4sample)1444 (invention)750.614589.415126 (comparative773.9212.0140.1sample)

Table 2 sets out the composition of the test solutions and the heat conditions in which they were used. The “saturated NaCl” and “sulfur flowers” test compositions represent extreme conditions to simulate the changes that a timepiece may experience during wear, especially in Asian climatic zones.

TABLE 2TemperatureTest[° C.]FormulaSaturated70Purified waterNaClNacl to saturation (at 70° C.)Flowers-of-505 L closed glass desiccator, with ceramicsulfurbase plate for Petri dish containing thesulfur flowers (0.1 g)Atmosphere with relative humidity of 75%,maintained by means of a saturated sodiumacetate solution at the bottom of thedesiccator.

The discolouration and tarnish tests were performed on washers made of gold alloys from Table 1 having a diameter of 20 mm and a thickness of 2.5 mm. The washers were successively polished with 320, 600, 1200, 2400 grit sandpaper up to felt containing diamond particles of 3 to 1 μm mean diameter.

For the saturated NaCl test, each washer was immersed in 200 ml of solution at the bottom of a closed bottle (Ø 65 mm, made of polypropylene). For the sulfur flowers test, the samples were placed inside the desiccator on the ceramic plate.

The washers were removed and rinsed to measure discolouration and tarnishing at different times during the test period and to observe the change.

The change in colour or discolouration ΔEiafter i days was calculated in accordance with the following formula:
ΔEi=√{square root over ((Li*−L0*)2+(ai*−a0*)2+(bi*−b0*)2)}
where L*, a*, b* are colorimetric values of samples measured with a Konica Minolta CM 3610 spectrophotometer (Illuminant D65, angle of observation) 2°.

The results of the discolouration test in saturated NaCl solution at 70° C. show that the alloy No. 1444 of the invention discolors significantly less quickly than the alloy No. 3N, which is a comparative yellow gold alloy, the alloy No. 2N, which is a comparative pale yellow gold alloy, and the alloy No. 126, which is a comparative 18 carat red gold alloy, of the prior art in this saline atmosphere. These results are illustrated inFIG.1, which shows that the variation in ΔE between prior art alloy No. 3N and alloy No. 1444 according to the invention changes from 2 after 2 days to virtually 2.5 after a period of 7 days.

The results of the tarnish test in sulfur flowers at 50° C. show that the alloy No. 1444 of the invention tarnishes significantly less quickly than the alloy No. 3N, which is a comparative yellow gold alloy, the alloy No. 2N, which is a comparative pale yellow gold alloy, and the alloy No. 126, which is a comparative 18 carat red gold, of the prior art in this sulfur atmosphere. These results are illustrated inFIG.2, which shows that the variation in ΔE between prior art alloy No. 3N and alloy No. 1444 according to the invention changes from 3 after 2 days to virtually 4 after a period of 7 days.

These tests therefore clearly show that the resistance to discolouration and the resistance to tarnishing of the alloy according to the invention is considerably improved compared to the 18 carat gold alloys of the prior art in saline and sulfur atmospheres.