SG Bijouterie-Joaillerie does not use 9k gold for the following reasons:
As it contains half as much gold, a 9 carat jewel will tend to be a little harder than 18 carat. However, it will be less solid (harder = more brittle) and therefore more sensitive to shocks and the pressures reproduced.
As for its wear, the higher alloy of other metals promotes oxidation and can cause it to lose its shine more quickly. It will also be more sensitive to chemicals, perspiration and water.
Generally, a 9-carat gold jewel is less resistant to time than 18-carat, which remains the most widely used gold for high-end jewelry.
