Okay, checked the Finch book at Lowes on lunch break. It's the newest (1997) edition. On page 120-121 in the TIG section, it mentioned that shielding gas may improve the weld appearance on the back side but it doesn't add any more to the weld integrity. It goes on to say that Al does not pick up contaminates in the air as much as Titanium or Steel do, and that molten Al cools in the presence of oxygen with only minor surface oxidation. Therefore, the use of shielding gas is a waste of money and resources.

My Finch book is an earlier edition (1985?), but I remember it said pretty much the same thing. When I first bought the book I was only interested in MIG and MAW, so I didn't read the TIG section much. I had read in product manuals and spec sheets that Argon is required for welding Al, but I guess it doesn't necessarily apply to TIG?

Needless to say, I'm thoroughly confused.