He told me I could rejuvenate the old one by heating it red
hot with a torch, then quenching it in water.  He said he hadn't bought
a new one in years.

Bob,

 The technique described is ok, but you will have better luck simply allowing the copper to cool in air rather than quenching it. That gives a better annealing and does work fine. I remove the scale created with a Scotchbrite pad.

Bill Jepson