I used to use a technique similar when wood working that I learned while stationed overseas. You can get a burn pattern that simulates burl wood by taking a bucket of really thin mud and slinging it on a piece of wood. You don't want to totally cover it, make it look like a car splashing through a mud puddle. Once the mud is splashed randomly over the wood, you use a torch to darken the wood from end to end. The wood doesn't burn were there is mud and in some places where the mud is thinner it darkens less. After you finish, you just clean the board with water and a wet rag. The end result looks like a dark burl wood. I would think it would look good on a bow.
