Catsup or Ketchup work the same as vinegar for the same reason. You could use lemon juice, dill pickle juice or a nice old Chianti with the same results. It's the acetic acid. So you might as well use the cheap version and find a small bottle of vinegar. Of course if you never use it, and you always have catsup around the house, maybe that IS better? lol

Have plugged shower heads? Old trick, get cheap vinegar, put in a small dish (don't waste) just larger than the shower head. Pour it deep enough so the nozzles can soak for a few hours. Replace and all that scale and crud will be gone.

Whatever, someone else pointed out the more important part. Dry the token with a soft rag and make sure it's dry, or you will have more tarnish.

I didn't see the oven part, but it makes sense, just on the lowest setting. In fact for those with "old fashion" ovens that have a pilot light. That is enough heat to dry things very well.

I'm sure just putting the token out in the Sun would be enough. No need for overkill.