I think that looks great DoW! Really Orky, which is the main thing with Orks! I really like the bare metals in particular. The weathering is brilliant, with really believable chips and bare metal parts. I think that is executed really well. The Ork looks fantastic - good skin tones and colour contrasts really help to add a good focal point to the model. The blue/white 'camo' is also really nicely done.
Excellent work all round DoW! Keep it up!
I am definitely no expert but it looks good to me. They only thing I would say is that usually paint chips are painted as if you can see the bare metal underneath the chip but on your rotors it looks quite blue where the paint has chipped. This gives the effect of peeling paint rather than chipped paint I feel.
Yeah, you'd normally have the first layer of weathering being the 'base' colour. That is, whatever was painted first onto the model before the blue or white was added. With Ork (and most tbh) vehicles, a small amount of black or brown usually fits best. That way, the initial scrapes represent the top layer of paint coming off. Then, within that weathering, you use a little silver. That represents all if the paint being damaged until only the bare metal shows.
I think DoW has done a really nice effect though, totally in keeping with the style of the model.