Don't bother with "patina" metal". Have a sheet metal shop bend a new piece to the dimensions you need, paint it with white vinegar, and toss it out into the weather for a few weeks. "Instant Patina" and it won't give you as many headaches when welding it into place.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!