Sort of a tutorial. Airbrushed: Retributor armor, then Retributor+ Vma steel, then another layer adding more steel. Shadows, airbrushed: Vallejo brown ink, or Pebeo Portrait pink, then airbrushed Daler rowney/Pebeo Sepia ink.

Kevin's Miniatures & Hobby Table: Tutorial: Weathering Metal Armor

Vallejo Airbrush & Weathering Techniques Book : Arts, Crafts & Sewing

How to Professional Airbrush Pre-Shading Shading and Highlighting Effect Easily

Airbrush Basics Metal Effects #tutorial

Airbrush Basics Metal Effects #tutorial

Shadowing and Texturing Armour

Armorama :: Vallejo Acrylics AFV Painting Systems Review

New to Airbrush - Retributor armour? : r/ageofsigmar

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Retributor Armour - Citadel Base : : Toys & Games

Contrast paint over Retributor Armor spray has awesome results! : r/Warhammer