I am a huge fan of AIM's weathering chalks. They are perfect for weathering but also may be used to add color to wood, plastic and foam structures. Grimy Black is great for adding soot, but also adds dark highlights to all wood, plastic or foam structures. I also use it on black construction paper to make it look like tar paper on roofs. I prep all my styrene model pieces with a light grey paint, then use AIM chalk to add all colors except white. White chalk can be used to age asphalt and gravel roads. Do yourself a favor and add AIM chalks to your modeling gear in Red Rust, Dirty Yellow, Grimy Black, Light Gray and Dirty White.