Alloys are used to harden ductile metals (a mechanical property of metals describing their ability to deform, stretch, or thin without breaking).
In an alloy, the main metallic element, i.e., the largest part of the mixture, is called the "base metal".
Elements intentionally added are called "alloying elements" or "additive elements," and unwanted elements are called "impurities."
Pure 24-carat gold is a ductile metal, meaning it is quite soft and cannot be worked pure in jewelry.
Pure gold is mixed with other metals, precious or not: silver, bronze, copper…
Depending on the added metal, gold takes on different colors.
Depending on the alloys, jewelers apply different hallmarks that allow them to be quickly authenticated.
Alloys - photo credit - fonteacireperdue.com-matières
Gold Alloys
Since 1994, only 18-carat and higher jewelry are allowed to be called "gold."
This means they are made with an alloy of 750 g of gold per 1000 g of metal.
Their fineness is then said to be 750/1000.
Jewelry made with 9-carat or 14-carat gold is allowed to be called "gold alloy."
Composition of gold alloys
For 750/000 gold jewelry, the remaining 250 g of additional metals give the gold a particular hue.
yellow gold comprising 125 ‰ silver and 125 ‰ copper;
rose gold comprising 90 ‰ silver and 160 ‰ copper;
grey gold (or white gold) containing, among other things, 250 ‰ nickel or 250 ‰ palladium;
red gold comprising 250 ‰ copper.
blue gold comprising 250 ‰ iron or cobalt;
green gold comprising 250 ‰ silver (the "recipes" may vary)
purple gold comprising 250 ‰ aluminum
Add photo palette of gold colors
In France, jewelers prefer to work with 18K gold.
While 9K or 14K gold jewelry is harder than 18K gold jewelry, it is also less durable.
Pieces made with a gold alloy oxidize more easily, react faster to perspiration and chemicals, and are more fragile in case of impact.
To identify the fineness of a gold jewel, simply check its hallmark.
On the other hand, 9K or 14K gold-plated jewelry costs less to buy due to its composition. They will also resell for less.
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In some cases, the color is not obtained through an alloy of metals, but through the deposition of a plating that gives it a superficial color on the surface.
Rose gold: Alloy composed of pure gold, silver, and copper.
Grey gold: Alloy composed of pure gold, copper, nickel, and zinc.
Green gold: Alloy composed of pure gold, silver.
Blue gold: Alloy composed of pure gold, iron, and cobalt.
Purple gold: Alloy composed of pure gold, aluminum.