Revamp all that old copper with vinegar and salt. The salt may seem like an abrasive but it is softer than the copper but hard enough to cut through that oxidization. Put the salt on first, then add the vinegar. Some tutorials say used lemon, I found vinegar worked better and was more affordable.
For old caked on tarnish, make a vinegar and baking soda paste and let sit for 20 min. Try not to use any abrasive scrubbers, as they can leave marks on the metal.
If you are looking to get rid of the protective varnish on the pot, you will need to boil the pot in a baking soda solution for about 20-30 min, it should peel off. However, it will allow your pot to tarnish more easily.
You can always send it away to be revamped and re-tinned. These are excellent pots to keep in the family and conduct heat extremely well.