24 vs 18 carat gold
The rings in the chain and the Mene plate are 24 carat, while the clasp is made of 18 carat alloy. The clasp needs to be strengthened by alloying it, for frequent handling.
Note the difference in color between pure gold, that is gold yellow, and the golden, metallic color of the alloy. No alloy can match the natural beauty of pure gold.