here some tests I did using free scanned models from http://threedscans.com/,
it's all isl based, since I can't write ISL from scratch, I hacked all codes from material's database and codes found in the forum.
The idea is to smear, add dirts, damage by water, give appearence to polish non_homogenous manner.
It's basically some multi-coating shaders blended together
have a super day
EDIT :
a variation tweaking snow/rough shader, I add color's pickers for shades and try differents function in Zangle, I can't get a gradient in x direction by now...





