So I recently discovered how to pull this effect off when I flicked through a copy of the Games Workshop’s ‘How to Paint Citadel Tanks’. In the book they show some pics of Nid Bio-Acid damage done to some Imperial tanks and described the process.
I decided to apply this to the Death Company Drop Pod I’m working on. I placed the acid damage high up on the pod petal purely for aesthetic reasons (alternatively you can picture a Gargoyle high up, getting a passing shot at the pod as it hurtles past!). I also decided to have the acid eat through to the interior a bit….
The method for it is pretty easy, I drilled some holes into the area I wanted affected by the acid, gave it a brush with a 50:50 mix of chaos black and boltgun silver then used warlock purple over the area that the acid hit. When that dried I highlighted some of the holes with tentacle pink. Finally I coated the area (well, splattered) with water effects paste. After 24 hours that was the effect.