design is nice, good job on that.
You are off with your color - you use a blue, while mos tof these shields rather were made out of low quality steel or iron. Iron has a reddish color to it and some natural warmth.
Then I would go with reflected light, because metal tends to be highly reflective. It'd help to get some references and try to paint after those.
DON'T USE DITHER FOR METAL! Just don't. Really.