It might deaden it a little. One of my students has engraved a few of them. My instincts told me not to do it, but my wife really wanted her initials on hers so I caved in. About 15 seconds into it I started cursing and didn't stop until I was finished. Lots of broken gravers and resharpening. Give it a go. It's not impossible, just not fun. Maybe you'll have a more pleasant experience. Like I said, I'm spoiled with softer metals and I'm not as fearless as I used to be
I think they're just a vacuum type of double-walled tumbler, made out of some crummy stainless, from what you've described. I wonder what the wall thickness is, just as someone's ready to ruin one by punching through it? Maybe diamond drag would be better!
I understand that the tumblers are 18 gage steal. My life is way too short to start hating what I find enjoyable. So I choose to pass on this one.
Thanks to all who responded, at 13 years old I knew nothing but thought I did, 17 years old my parents knew nothing, 21 years old the world was mine for the taking if they will just listen to me darn it. At forty, hey mom and dad do know a few things and now at 55 plus years I am worse off than when I was six because I ask when I am not sure, I just can’t understand were common sense went to in the world, and thank the good lord that I have a few friends that I can ask a question to.
Skill comes from diligence.
Merry Christmas to all and a happy New Year’s.