I was hoping you would be willing to share how you went about painting the black on this Sanguinary Guard model. Looking at some WiP pictures from this battle report and your description for this eBay bid get the impression it is a base coat of light grey* followed by a couple of washes. Similar to what Dezartfox did here.
*Something like Army Painter's Uniform Grey.
My usual method of painting a mini intended for tabletop play is to first undercoat them in a mid-tone gray. For this, I currently use Tamaya neutral grey model aircraft spraypaint (expensive, but very detail-preserving with a smooth finish).
After the model dries, I then hit them with a brown or Devlin Mud wash to bring out the detail and make them presentable on the tabletop until I get around to painting them properly.
Once I'm ready to paint, I work from dark to light. The brown wash allows me to preserve some definition lines by simply not pushing paint into the crevices that I want to remain dark. If I used black for this, it would kill the color. But the brown accentuates without overpowering the color. Much as fine art painters have done for hundreds of years.
After the base colors go down, I start shading lighter with 2-3 layers of lighter colors. The lighter the color, the more layers you need. Usually, it takes around 3 hours per model to paint this way.
Now if I feel like spending 6-7 hours per model, I'll just paint the base colors over neutral gray without the brown wash and do individual colored washes for each base color, which I then re-paint the base color over before I start shading to light. This gives much more subtle results (and great skin tones), but takes forever.
And yes, I did hand paint those mugs on the shields. :)
Which brings us to that Sanguinary Guard model...
I originally did do the grey undercoat + wash on these guys. But when I decided to do "black" armor, I simply painted over everything that was there without trying to preserve the dark lines in the cracks. What you see is more like the dwarves above. Custom washes over a base coat.
Because the thing about painting black (or white) is to never actually paint black (or white). Instead, you want to paint a NEAR black. Meaning an actual color. Because real black will suck the life out of your model.
So what I did was paint a dark cyan over most of the model, and then wash it twice. Once with a blood red wash, and then once more with a black wash. Then I painted the original dark cyan over the washed areas, leaving the darker cracks alone. Before I came back in with 2 lighter shades of that dark cyan base color.
The wings, head, and the base were painted ice blue, washed with red + black, and then I came in and layered white over the top. It looked ugly as hell until the white was on, but then it all came together.
This test model took 2-3 hours to paint, but now that I've got the process down, I expect the rest to take about 1 hour per model if I airbrush the dark cyan on. Which is pleasingly fast. :)