That is the inch and a half wide business end of a warhound titan Inferno Cannon. This thing is capable of incinerating dozens of the enemy with every burst so it had to look serious! The picture above is the final effect incorporating soot, oil and other muck. The first step was getting the metal to look regularly heated.
Adding oil and soot was simple, a 3:1 mix of brown and black ink built up in layers creates the thick oily colour you are after. The more layers you put on the less like a stain it looks and the more like a leak. Still need to touch up some of the tank banding in this picture but otherwise its done! The soot was Forgeworld Soot Black weathering pigments flicked on to some odourless thinner (essentially posh white spirits) and then spread out with a dry brush once the thinner had dried out.
While we're talking white spirit lets have a look at the picture above. This is a very simple technique to create a rusty surface rather than the rusted surface that JeffRust creates. I painted AK Interactive's Rust Streaks liberally all over a Leadbelcher basecoat. This is an enamel paint designed to allow various weathering effects over an acrylic basecoat. Once the Rust Streaks was painted on I used a brush soaked in odourless thinner to thin the paint in situ and drive it into the recesses. It is this post-painting manipulation that enamels are good for. They are useless for normal painting. Put it this way, I did this at about 10 this morning. It is now 3.30 and it is still not dry. Use enamels with caution! Anyway, I'll leave you with a view of the rear end of the Inferno Cannon and return to the titan painting!