Hi Kratos,
there are a few methods you could use, but heres what i would do if i wanted to paint scorch marks on armor
1. mix a very small amount of chaos black into some scorched brown, just to take away the kind of red colour you get from scorched brown.
2 water the paint down so that it becomes translucent, just very slightly thicker than if you were using it for a wash
3. add a dab of dish soap
4. ok take a small amount of paint onto your brush and fill in the area you want to look scorched, imagine this to be the outer ring of the scorch mark pull the paint out thin on the model to blend it into the underlying armour colour
You may need to repeate this once or twice to get the desired effect.
5. get some chaos black on your pallet and add a touch of scorched brown, it should still look pretty much black but using black on its own looks unnatural
6. stipple the area that would have recieved the brunt of the scorch, this part is simulating soot
7. final bit... by now you should have a brownish black translucent outline to the scorch and the middle should be black like soot, stipple a bit of pure scorched brown around the outside of the black soot part, this should blend it into the translucent ring.
Hope that helps or at least gives you a few ideas, you can ad other colours to the mix if you want it to pop, like vermin brown or even a bit of watered down orange, or desert yellow just mess about and have fun.....Good luck:beer: