Did some practice on the Shield's Underside of the Hobby Star MG 1/100 Astraea Type F Avalanche on how to do weathering on panels.

Weathering means that you'd paint the Gundam to look like it's already old and battle-worned.

What I did here was very simple and involved just using a metallic sharpie and black acrylic paint. The Sharpie was applied using cotton buds and the acrylic was dry brushed onto the surface.