The number in the sample means the share of pure metal in the foot, expressed in per mille, i.e. in 1 gram of gold, sample 585, there is 0.585 grams of pure gold. The remaining part (0.415 grams) is a ligure, or alloy additions. They are carefully selected metals, which not only reduce the share of gold, but above all improve the properties of the finished alloy, providing the desired mechanical parameters.

The composition of the ligature is also responsible for the color of the gold alloy. Ligatures for white gold change the color of the alloy to white, even though we used pure gold in yellow. Traditional so-called red gold contained a large amount of copper. Currently, the composition of the ligature is the secret of its producer. A lack of sensitizing ingredients (eg nickel) is guaranteed for this.
The equivalent of the gold 585  is 14-carat gold (in this system pure gold has 24 carats).