After working on the big 19th century cast iron pot since Sunday, here are the results so far. It doesn't look too bad – far from flawless, but in workable condition. I think it's time to season the pot, tonight. The Google search was correct, as I can barely see a logo on the bottom that looks like "MAR" "TC C Co" "A". The middle part definitely stands for "T&C Clark & Co." I'm not sure what the "MAR" is - month of manufacture, maybe? The "A" must be a model type or a mold number.
September 20, 2013, pdate on the huge 14-quart 19th century cooking pot: I've been informed this pot is from the cast iron foundry at Marietta, Pennsylvania; it's not from England as I first thought. My biggest concern for this pot is whether or not the enameled interior contains lead – if it does, then I can't cook with it. So, on Monday I'll be bringing it to a professional lead testing service, and they'll use an X-ray gun to examine the enamel for lead. The results will be interesting, regardless of what happens.