US 12,252,769 B2
Timepiece or piece of jewellery or gemstone jewellery made of gold
Alban Dubach, Bienne (CH); Gregory Kissling, Macolin (CH); Stephane Lauper, Cortaillod (CH); Denis Vincent, Neuchatel (CH); and Gaetan Villard, Cossonay (CH)
Assigned to Omega SA, Biel/Bienne (CH)
Filed by Omega SA, Biel/Bienne (CH)
Filed on May 15, 2019, as Appl. No. 16/412,476.
Claims priority of application No. 18175618 (EP), filed on Jun. 1, 2018.
Prior Publication US 2019/0368005 A1, Dec. 5, 2019
Int. Cl. C22C 5/02 (2006.01)
CPC C22C 5/02 (2013.01) 14 Claims
 
1. An 18 carat red gold alloy, consisting of, in weight percent:
75 weight % to 77.5 weight % of gold;
0.5 weight % to 3 weight % of palladium;
10 weight % to 18 weight % of silver; and
7.5 weight % and 9 weight % of copper;
wherein the respective percentages of all the alloying elements add up to 100 weight %, and wherein the alloy is zinc-free, germanium-free, nickel-free, cobalt-free, and indium-free,
wherein in a discoloration test in a saturated NaCl solution at 70° C. AE of the alloy changes from 1 at day 1 to greater than 1 and lower that 1.5 at day 7,
wherein the discoloration ΔEi after i days is calculated in accordance with the following formula:
ΔEi=√(Li*−L0*)2+(ai*−a0*)2+(bi*−b0*)2
where L*, a*, b* are colorimetric values of samples measured with a spectrophotometer.