Only dawn dish soap. And not allot of it either. The only thing I can think of was that I let them soak once for a couple of hours.
If you have hard water, it contains alkalies... That "could" account for the etching.... Adding a small amount of vinegar "can" counter act any alkalies... I use vinegar to clean out the deposited alkalies in my coffee pot... I also add vinegar to my Sous Vide to stop the deposition of alkalies on the element and associated parts....