queen_annes_revenge wrote:
you'd probably be better using a rust streaking grime for night lords. the dark blue of their scheme wont take either of the normal streaking grime variations well, and will likely just end up looking messy. even their lighter streaking grimes, which would be more visible, wont look that nice because of the green laid over the dark blue would be very jarring.

With weathering, as a general rule, darker base schemes are generally weathered using lighter colours for panel lines, streaks etc, as opposed to lighter schemes which will have darker panel lines and effects.

ak do a rust streaking fluid, and also a couple of naval streaking fluids that are a rusty brown. This would work quite well as the orange would give a nice complimentary contrast with the blue. If you didn't want rust you could also try their naval salt streaks, or rain marks, which will give you a lighter effect.

I don't want to patronise and obviously I don't know how much you know, but bear in mind that Ak fluids are enamels and need mineral spirits to thin and work with. you use a brush to apply thin lines of the fluid down the surface youd like the streaks on. let them stand for 10-15 minutes, then using a flat brush with mineral spirits, pull it down the streak lines to blend them out. they are a very good tool. using them on space marine armour is possible, it just requires a very steady hand and an eye for detail work.

 queen_annes_revenge wrote:
yeah, a dark oil wash would work on them, as long as it was in their recesses.

the problem youre facing, is that because their armour is already dark, if you apply a dark weathering scheme to them, you're going to destroy any contrast you have on their highlights. if you wanted to suggest a burned look, you could try getting a grey ash pigment, and putting it in the recesses around their boots. combine this with some thoughtful basing and you could easily get the effect of them in a burned city.