The practice bombs I use in my Blitz lamps are cast iron. Something I didn't know about cast iron until I started using it, is it can shatter. Like pottery, except with fewer pieces.
A while ago, one of the practice bombs arrived with part of the fin snapped off. The missing piece wasn't in the box, and the rust along the broken edge told me this wasn't a recent occurrence. For all I knew, it could have happened when the Navy packed it up at the end of WWII. And it was conspicuous enough that I couldn't make it into a standard lamp and sell it. Not without a discount and disclaimer, anyway.
Instead, I used it to try some new finishes. There are dozens of patinas and treatments available for iron, from traditional blackening agents invented centuries ago, to unusual chemical blends that require electrical current or heat to apply. I found the perfect finish in the middle: Sculpt Nouveau's black magic, a traditional black patina made with a modern chemical formula. It brought a deep, rich black out of the iron, a color that reminded me of cannonballs and old ships with hand-forged nails.
While the burnished gunmetal finish of the original Blitz is clean and modern, the black version looks ancient and industrial and somehow more menacing. I've offered the prototype for sale (broken fin and all) (update:sold) and in 2013 I'll be offering Blitz lamps with both finishes.