Stonewash/smokewash

[running bird]

I was wondering if anyone had tips on how to get a "smokewash" look when stonewashing a knife? I thought maybe adding coal in with the stones but wasn't sure if that would do much or if it would even work.

Also do you think a stone washed sword would look good? and how would I go about doing that? I don't know what size or what kind of container I could stone wash a sword in, cuz swords tend to be a bit bigger than knives. Just a little.