theres a chemical process you can use to instantly rust it. its a combination of muratic acid and hrydrogen peroxide. you can get a life time supply for like 15$ at a hardware store...
look it up on google. i got some from a friend thats was premixed..
i think you want like 5% acid and let it sit for like 30 seconds then hit it with the peroxide. and repeat, then flat matte over the top
its what i used to patina bikes i built.