Howdy , Hagoth 
I'll go that route ---- just let the grime fall where it wants on it .
I added to it with a wash of raw umber and then the orange - plus some pastels rained down in a dusting while it's still wet (ish) ( most of the powder will get knocked down after it dries . I'm just going to keep layering until it looks funky enough )
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& I need to ' burn-up ' the engine bell and thruster nozzles :
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