Hi Greg,
It's a big relief to me to see that you've done your homework on safety. When I saw where you said you'd nicked the steel with your fingernail I really panicked...
Here's my only additional suggestion for now: If you're using rebar for armatures for artwork I suggest you at least consider getting some mild steel round stock. It is surprisingly cheap even though steel is high. It is easy to heat and bend. If you weld it you can reliably get it to stick together without potential problems.
Metinks it would be a pity for you to spend a lot of time on a successful sculpture only to have it break apart at the welds. In construction work, while welding sections of rebar is not unheard of, it is discouraged. And where it is welded the codes call for a healthy overlap, backup pieces, pre and post heat, as I understand it. I don't mean to imply that I've read any of the codes.
But check > Vernon,