John,
You are in the wrong business whatever it is. You need to buy yourself an old bus and then sign up people and take them all over visiting thrift (or antiques) shops. Of course you have to charge them for the bus ride and tour. Using your computer to find the thrift shops is pretty cool. Have you lined up a booth in a mall so you can sell all the stuff you are going to quickly accumulate? Or a big barn to store it in? Being addicted to this hobby can cause big troubles but with big fun, too.
Fire rings? No, don't know a thing about them. But I do know about "heat rings" which are the same thing only with a better name. A skillet with a heat ring does not mean it's old. Lodge has always put a heat ring on their pans. Even some very old, mid-19th century skillets have smooth bottoms without heat rings, although most such pans do have heat rings.
Better ways to estimate ages of skillets and other pieces are by subtle details like pouring lips, handles, casting quality, amount and style of writing on the bottom, "made in USA" (mostly post 1960), etc. Larger pouring lips (compared to today's baby lips) are a mark of an older skillet. Some very old pans had huge lips or, usually, a single lip but many did have small lips, too. Casting quality was usually better and smoother on older pans. Writing on older pans is larger, deeper, wider, better quality. All of these things come in time by looking at a lot of iron and making mental notes. Get the good books if you don't have them (Dave Smith's blue and red books), visit other collectors, go to our convention, and keep asking questions here.
Steve
