Hi Byron It's always good to hear from our metal detecting visitors. Sounds like an interesting site you've been working on in Whyalla.
The reason that an old brass ring you dug up may be marked is because it could have been originally a gold plated ring. A lot of gold plated jewelry is marked. This electroplating process involves a very thin coating of gold applied over a base metal. The electroplating process began in the 1840s so consequently some very old electroplated rings can still be found.
