1) Basecoat the mini with chaos black, I have used the Chaos Black Spray paint but I'm sure the potted paint will work just as well. I didn't take a picture of this stage, everyone knows how to do it.
2) A coat of Adeptus Battlegrey is given to all armour areas.
3) A 50/50 mix of Vallejo USMC Tank Crew (from the Panzer Aces range) and Astronomican Grey is painted over the armour.A couple of thin coats should be enough.
4) Wash the recesses where the armour plates meet with Badab Black and paint any cabling and details (studs, eye lenses etc) Chaos Black.Allow the wash to dry.
5) Using the above mix, paint over any areas that were covered by the wash but shouldn't have.Be careful to leave the previous washed layers showing in the recesses.
6) Hightlight the armour with a 30/70 mix of USMC Tank Crew and Astronomican Grey.
7) Fine highlights are added to the edges of the armour plates using a 30/70 mix of USMC Tank Crew and White.
8) Metallic areas are painted Chainmail, washed with Badab Black and then highlighted with Chainmail.
9) Any gold areas are painted Dwarf Bronze.
Gold areas are painted over with Vallejo Brass, washed with Devlan Mud and highlighted with 50/50 Vallejo Brass and Mithril Silver.
The eyes are first painted Mechrite Red and then highlighted with Blood Red, Iyanden Darksun and finally Skull White.
The Eye of Horus is given a couple of thin coats of Iyanden Darksun, highlighted with 30/70 Iyanden Darksun and White and then the pupil is added with Chaos Black.
The circle around it and the seal of the Oath of Moment (Purity Seal) are painted Mechrite Red and highlighted Blood Red.
The Oath of Moment itself is painted Scorched Brown and then highlighted with Snakebite leather, Dheneb Stone and Skull White, leaving a little of the previous stage showing every time.
Battle damage is painted on with Chaos black and little dots/lines of Astronomican Grey are painted under it for highlights.
The Bolter's metal parts were painted like the other metal areas and the casing was highlighted with Adeptus Battlegrey and Codex Grey.
11) Paint the base according to your liking and your Sons of Horus marine is ready to fight for the Warmaster!