Hmmm, grey metal would suggest an aluminum alloy. Lot's of older ones were very thick. So don't use oven cleaner just in case. Try a magnet test to see if they are iron. But an old iron pot is usually black.

Try boiling some vinegar in them, or cooking an acid fruit such as rhubarb.

Also you can clean them with wet or dry rubbing down paper from an auto parts store. Try 400 grade first and use it wet with detergent. Then, when you have got them clean, you can shine them up with 600 grade or finer. I have to do this regularly at home with both stainless steel and aluminum pots, 'cos some lazy bugger (often me) lets them burn.