No problem guys, glad you find it usefull!
Yes, I guess charcoal would produce the same effect.
Sadly I have only had god results with the colored ones on light surfaces. it's seems they are to transparent to be used on darker objects.
I don't think it sticks to a Marmit trooper, but you could spray it with a thinn coat of flat clear and then weather it. Use a satin coat to seal it after and you'll get the same finish as it was before.
Steve.