"Oh, you know," Tony said, reaching across, tapping something, and watching a gauntlet condense around his hand.

"This and that."

Like he said: High tech nanotechnology. Once you had the basic building blocks, all you needed to be able to do was tell it what to be.

And have enough of the right kind of material around for them to build themselves out of, of course. Also probably wise to avoid that whole grey goo scenario, but it wasn't as if he was Justin Hammer.