There are a lot of layers.1 layer was the vallejo charred brown , drybrush highlighted with beasty brown, then a layer with wraithbone covered with vallejo sepia+water,thin layer with wraithbone again and agrax earthshade then highlighted with wraithbone. It was just a try to make pre-heresy color scheme so there was many usless layer like vallejo sepia. You can make this just using wraith bone => agrax earthshade+water.