What's the general rule on deciding whether to use Devlan Mud or Badab Black to wash a specific part? I was under the impression that colours that lean toward red should be washed with Devlan Mud (reds, oranges, yellows, browns, creams) and other colours should be washed with Badab Black (grays, blues, greens). Is it not so? Why wash Sigrid's reddish fatigue with Badab Black instead of Devlan Mud, I'm still trying to understand the logic behind this whole thing.
Also, you say "just a bit, not too much". Well, I was doing some tests on some ammo crates and my conclusion was a bit of a paradox: If I applied only a little bit of wash, spreading it around, it would quickly dry and wouldn't really flow much towards the recesses, so pretty much the whole surface became all smudged. Not very dark, but not clean at all, stained all over. If I applied a lot of wash, really allowing it to create pools on the surface, it would dry slowly, flowing towards the recesses and leaving the overall surface apparently cleaner and more uniform, however the recesses would be pitch black. What's the secret?
I'm really scared of ruining my painstaking base colour work when doing the washes. Though I do have a bit of a safety net. Since I painted with enamels, I think I could wipe off the wash with alcohol if it turns out ugly, without affecting the base colours, which are only soluble in paint thinner.