The black/red is a bit of a story...
So the black is just the black primer and the red is mephiston red and evil suns scarlet. The first technique i tried was to use glazing medium and mephiston red. I had bought a bottle of the medium and really wanted to try using it (had never used it before). I
First attempt... I thinned the red with the medium and also some water since i tend to use a wet palette. I started doing the rib cage of the juggernaut by just trying to glaze the edges with the thinned red in order to get the transition. It was working ok but not great, i was getting too much red too far from the edge. I also did the front leg facing the camera in the last picture towards the end of this session and OH MAN it worked perfectly. I was really excited that i had finally gotten it. Unfortunately i was never able to recreate the effect quite as well and became dismayed. I think i just had the perfect mix of water, medium, and paint when i did that leg and i couldn't hit on it again.
Multiple later attempts... I wasn't able to recreate the smooth transition i got on that first leg so i started trying to use just paint and medium of varying thiness and what i got was a fade that was still not very good. All of the black that you can see now was a faded shade of pink...needless to say, that was Khorne approved. So i cleaned it all back up by painting black back over it and basically starting again (except for the one front leg).
The technique i hit on that worked really well was to simply use a thin coat of mephiston red to stripe the edges, followed by an edge highlight of evil suns, followed by a couple layers of very water thinned mephiston to create a small area of fading. After i did that on all of the edges, i washed the whole thing with nuln oil. This was the magic trick, it mellowed all of the stripes and made the fade work. I then did a super light dry brush of mephiston over most of the model to put an ever so slightly red hue on the ridges and crests which you can't see very well in the pictures.
The gashes in the jugger's armor are mephiston and evil suns after the nuln oil so they were not darkened/mellowed by that step. The jugger's head was much simpler, just mephiston, washed with nuln oil, highlighted with mephiston, evil suns, and wild rider red around the eye.
Thus is the tale of the black/red