Может ли кольцо все еще быть настоящим золотом, даже если нет маркировки?
Да, это возможно. Это может предшествовать маркировке, возможно, размер был небрежно подобран, а маркировка вырезана., маркировка может стереться, есть множество причин отсутствия маркировки. The only way to know for sure is to have it tested. If it is real, you could have it marked, or obtain a certificate of authenticity from a qualified expert so this doesn’t come up again. And also so you have proof that it is real. Удачи!
What is the difference between a titanium steel plated platinum ring and a 925 sterling silver plated platinum ring?
Both are probably fictitious. Who would put a titanium plating over platinum, or sterling silver plating over platinum? You put the precious metal plating over the inferior metal.
Should I wear a gold ring with an amethyst stone?
Normally one should wear amathyst in silver for astrological purpose. If you are wearing it in general you may wear it in gold.