I have a La Rochelle gold bracelet and was wondering if it was solid gold or dipped the marks on it are CT 18750

Yes,by the mark it is 18kt solid gold .It is marked with the cartage system. Usually older pieces or European countries use this style of marking 750 means 750 parts out of 1000 so it is 75%pure gold . Americans us 24kt as pure , 18kt as 75% pure ,14 kt is around 53.135 pure not quite sure on the decimal. It is just a different way than most people are used to seeing.I hope that helps