|Left to Right: Blood Raven Dreadnought, IG Sentinel, Tau XV8|
The Sentinel is pretty much the opposite - I don't see IG machines getting a lot of time in the body shop and much like their crews I think they get kept in the field pretty much until they fall apart. So the Sentinel is chipped and worn and streaked with dirt and oil; quite by chance I found that dry-brushing back over the unit stripe on it's "cheek" makes it look like the paint is wearing off back to the basecoat, and generally the poor bugger looks like he needs a rest.
Finally the Dread is sort of half-way between the two - the colour is built up of multiple thin layers from the edge inwards, so the flat sections of the hull are noticably darker in the middle even before I added the edge highlights. Its left him looking slightly worn and old without being covered in chips and scratches, as broadly speaking I suspect Marine gear is much better looked after than its IG equivalents.
And these chaps are the equivalent Infantry, with the same general principles in mind. Note the Guardian's Lasgun being the "wrong" colour for his urban camo, as fluff-wise I'm not sure the Munitorium is up to reissuing a whole regiment's weapons on re-deployment, whereas again the Fire Warrior is all nicely colour co-ordinated.
It does make me think that the next big skill I need is better photography though...