TIMEPIECE, PIECE OF JEWELLERY OR GEMSTONE JEWELLERY MADE OF GOLD

Abstract

A gold alloy may contain, by weight, between 73% and 77% of gold, between 5% and 11% of silver, between 1% and 7% of palladium, and between 10% and 18% of copper. The gold alloy may include iridium, rhenium, and/or ruthenium in up to 0.05 wt. %. The gold alloy may have an a* value in a range of from 3 to 9, and a b* value in a range of from 12 to 18, in CIELAB color space. A timepiece, piece of jewelry, or gemstone jewelry, may be made of such a gold alloy.

Claims

1. A gold alloy comprising, by weight: gold in a range of from 73 to; silver in a range of from 5 to 9.9% silver; palladium in a range of from 1 to 4.9%; and copper in a range of from 10 to 18%.

2. The gold alloy of claim 1, comprising, by weight: the gold in a range of from 73.5 to 77%; the silver in a range of from 5.5 to 9.9%; the palladium in a range of from 1.5 to 4.9%; and the copper in a range of from 11 to 18%.

3. The gold alloy of claim 1, comprising, by weight: the gold in a range of from 73.5 to 76.5%; silver in a range of from 5.5 to 9.9%; the palladium in a range of from 1.5 to 4.9%; and the copper in a range of from 11 to 16%.

4. The gold alloy of claim 1, comprising, by weight: the gold in a range of from 74 to 76.5%; silver in a range of from 6 to 9.9%; the palladium in a range of from 2 to 4.9%; and the copper in a range of from 12 to 16%.

5. The gold alloy of claim 1, comprising, by weight: the gold in a range of from 74 to 76%; silver in a range of from 6 to 9.5% silver; the palladium in a range of from 2 to 4.9%; and the copper in a range of from 12 to 15.5%.

6. The gold alloy of claim 1, comprising, by weight: iridium, rhenium, and/or ruthenium in up to 0.05%.

7. The gold alloy of claim 1, having, in CIELAB color space, an a* value in a range of from 3 to 9, and a b* value in a range of from 12 to and 18.

8. The gold alloy of claim 1, having, in CIELAB color space, an a* value in a range of from 5.5 to 8, and a b* value in a range of from 14 to 17.

9. The gold alloy of claim 1, having, in CIELAB color space, an L value in a range of from 80 to 90.

10. The gold alloy of claim 1, having a hardness HV1 in a range of from 140 to 185.

11. A timepiece, piece of jewelry, or gemstone jewelry, comprising: the gold alloy of claim 1.

12. The gold alloy of claim 1, having a hardness HV1 in a range of from 155 to 180.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0023] FIG. 1 shows a timepiece comprising a middle made with the gold alloy according to the invention.

[0024] FIG. 2 shows the discolouration curves for the alloy according to the invention (INV) and for two 18-carat alloys (2N, 3N) according to the prior art.

DESCRIPTION OF THE INVENTION

[0025] The present invention relates to an 18-carat gold alloy more particularly intended for application in the horology, jewellery or gemstone jewellery field. It thus further relates to the timepieces, pieces of jewellery or gemstone jewellery made of this alloy. The term timepieces is understood to mean both external components such as a middle, a back, a bezel, a push-piece, a bracelet link, a dial, a hand, or a dial index, etc., and components of the movement such as a plate, a bridge or a balance. By way of illustration, the timepiece is a middle 1 as shown in FIG. 1.

[0026] The gold alloy according to the invention contains, by weight, between 73% and 77% gold, between 5% and 11% silver, between 1% and 4.9% palladium, and between 10% and 18% copper. This alloy is free of nickel, cobalt, iron and manganese.

[0027] Advantageously, the gold-based alloy contains, by weight, between 73.5% and 77% gold, between 5.5% and 9.9% silver, between 1.5% and 4.9% palladium, and between 11% and 18% copper.

[0028] Preferably, the gold-based alloy contains, by weight, between 73.5% and 76.5% gold, between 5.5% and 9.9% silver, between 1.5% and 4.9% palladium, and between 11% and 16% copper.

[0029] More preferably, the gold-based alloy contains between 74% and 76.5% gold, between 6% and 9.9% silver, between 2% and 4.9% palladium, and between 12% and 16% copper.

[0030] In a particularly preferred manner, the gold-based alloy contains, by weight, between 74% and 76% gold, between 6% and 9.5% silver, between 2% and 4.9% palladium, and between 12% and 15.5% copper.

[0031] Moreover, the gold-based alloy contains, by weight, between 0 and 0.05% (inclusive) of one or more elements selected from among iridium, rhenium and ruthenium, the range 0-0.05% covering the total percentage of the one or more of these elements. Advantageously, the alloy contains, by weight, 0.0025% iridium.

[0032] To prepare the gold alloy, the various elements of the composition are melted down before being cast. The casting ingot is then deformed with a work hardening rate greater than or equal to 75% distributed in several passes with intermediate anneals carried out in a temperature range of between 550 C. and 750 C., for a time of between 5 minutes and 30 minutes.

[0033] In the examples hereafter, the samples are annealed at a temperature of 650 C. for 30 minutes. After cooling, the blanks are dimensioned, for example by machining.

[0034] The alloys obtained after deformation and annealing have, in the CIELAB colour space (in accordance with standards CIE No. 15, ISO 7724/1, DIN 5033 Teil 7, ASTM E-1164) an a* value between 3 and 9, preferably between 5.5 and 8, and a b* value between 12 and 18, preferably between 14 and 17, the a* and b* values together defining the hue of the alloy. They also have an L value between 80 and 90, the La*b* values together defining the colour of the alloy. According to the present invention, the focus is more specifically on the a* and b* values which define the hue of the alloy.

[0035] These alloys have a hardness of between 140 and 185 HV1, preferably of between 155 and 180 HV1.

[0036] Table 1 shows the composition by weight of a reference 9-carat gold alloy from the European patent application No. 19193469 and of five 18-carat gold alloys according to the invention. The measured colorimetric values and the measured hardness (HV1) are also set out in Table 1. The L*a*b* colorimetric values were measured with a KONICA MINOLTA CM-2600d spectrophotometer with a D65 illuminant and an observation angle of 10. The Delta E and Delta C values respectively represent the colour difference and the chroma difference, with respect to the 9K reference. The Delta E is calculated on the basis of the La*b* values as follows, where L.sub.ref, a*.sub.ref and b*.sub.ref refer to the values of the reference 9-carat gold alloy:

E=[(L.sub.refL)+(a*.sub.refa*).sup.2+(b*.sub.refb*).sup.2].sup.1/2

The Delta C is calculated on the basis of the a*b* values as follows:

C=[(a*.sub.refa*).sup.2+(b*.sub.refb).sup.2].sup.1/2

TABLE-US-00001 TABLE 1 Compositions (% poids) Colorimtrie La*b* D65 10 de couleur (La*b*) chromatique (a*b*) Duret Au. Ag. Pd. Cu. Ga L a* b* Delta E Delta C [HV1] 9K rfrence 37.6 6.4 2 50 4 87.1 6.7 15.0 0.00 0.00 131 18K 75.1 5.4 2.0 17.6 0 85.6 7.8 15.3 1.89 1.11 165 invention 75.1 5.4 2.0 17.6 0 85.9 7.7 15.3 1.58 1.02 175 75.1 7.1 2.6 15.2 0 85.7 6.9 15.4 1.42 0.42 161 75.1 7.3 2.0 15.6 0 86.0 7.2 16.4 1.88 1.50 169 75.1 7.1 3.3 14.6 0 86.0 6.4 14.7 1.22 0.43 158

[0037] The values of a* and b* are very close, with a* values between 6.4 and 7.8 for a reference value of 6.7, and with b* values between 14.7 and 16.4 for a reference value of 15. To the naked eye, the reference and the gold alloys according to the invention have the same bronze hue. Tarnishing was assessed visually after exposure to ambient air for several days. The 18-carat gold alloys according to the invention maintain their attractive bronze hue without tarnishing, in contrast to the 9-carat gold alloy according to the prior art, which tarnishes substantially. Moreover, comparative discolouration tests were carried out between the 18-carat gold alloy according to the invention and two 18-carat gold alloys according to the prior art, namely the alloy 2N, which contains, by weight, 75% gold, 16% silver and 9% copper, and the alloy 3N, which contains, by weight, 75% gold, 12.5% copper and 12.5% silver. The discolouration tests were carried out by immersing the samples in a water solution saturated with sodium chloride at 70 C. for several days. Discolouration, defined by Delta E, was monitored by colorimetry measurements carried out under the same conditions as those described hereinabove. As shown in FIG. 2, the new gold alloy shows a significant improvement in discolouration resistance compared to the 18-carat gold alloys 2N and 3N of the prior art.

[0038] The alloys according to the invention have a hardness HV1 in the annealed state of between 158 and 175, allowing them to be easily deformed.

[0039] The new gold alloy thus has an attractive bronze hue with lower tarnishing over time.