Well, Yutha was right. I discovered that Hazel Atlas started up around the turn of the century and closed in the early sixties. This mixing bowl originally came in a set of three (of different sizes) and was produced in the 1940s if my information is correct. I can't believe I found a beautiful 1940s bowl at a thrift store for a song.
I guess the moral of the story is this: if you're passing by a thrift store, it's always worth having a poke around. You never know what you will find and every vintage treasure has at least one great story behind it.
I'm all happy now. Time to learn how to crock.