I actually got a quite simular effect with a broken glas, worked for me...
the thing with the coffee is defintly a great idea, will try this on the lume, thanks.
I also thought about cigarett smoke, also gets your hands look real old after some years...
@Freddy333: thanks for the links, I already read this and instandly forgot the baking procedure, thanks.
I guess by 550 decrease you mean fahrenheit....
Did you grill it or did you use hot circulation air?