What!?!? And give away my trade secrets?!?!? Shirley, you jest!
Sorry. I couldn't resist yanking your chain just a little...
It's hard to list specifics on some ID's. I'm just guessing about that your items are not 100+ years old. But I've been digging and ID'ing relics for over a decade and you begin to develop an eye for things. If you pay enough attention, you begin to see patterns and similarities to conditions of metals and blah, blah, blah. What I'm trying to say is identifying this stuff is often more of an art than a science.
In the case of your relics posted on this thread it was mostly the amount of rust on the tongue of the brass buckle. Iron bits that size are often (not always) gone after 100+ years in the ground. Of course, there are all kinds of variables that can impact the oxidation, but you begin to 'get a feel' for those things with more experience. Am I always right? Hell no! If you go back and read some of my posts you'll see some pretty hair-brained claims made by me. But as I've gained more experience I've gotten better at figuring things out.
Bottom line - Many of those details you are trying to learn will only come through experience. So hang in there, keep digging, and keep posting here.