It's a problem for many modellers - to imitate muzzle burn on the weapons. They appear is the barrel gets really hot - for example, on machine gun, or on flamer. Such rainbow looks realistic and it's really better than plain soot. But how to imitate it? There are a lot of guides which suggest airbrush for it. But not everyone has an airbrush. For those who want it simple we have a really easy tutorial with Citadel washes.
Wash metal parts with Nuln Oil. We've also washed all the other parts with it.
Wait untill it completely dries, then apply Drakenhof Nightshade on the very tip of the barel. Don't make it too thick so that the metal could be seen through.
Use Druchii Violet to make the second stripe further from the muzzle, touching the previous layer a bit.
The final step - Seraphim Sepia. You need it not only to make the 3rd stripe but also to cover the other two with a very thin layer.
Here it is - looks much better than black soot, and it's really not that difficult!