(If needed:) Gray base. If your metal base isn’t gray, spray paint it with a light to medium gray. I used an actual gray spray paint, but I think a gray primer would work, too, which is easier to find.
Metallic silver layer #1. Add a dollop of the silver paint to a paper plate, dip the ends of the chip brush lightly into the paint and then blot it on the plate. Move to the painted metal surface and start pouncing the brush up and down in various places all over. You’re not going for full coverage here, but some areas should be more covered than others like the photo above.
Black layer. To add further lowlights, add black to the surface using the same method as the silver: adding a small amount to the paper plate, dipping just the ends of the brush and then blotting on the plate so the brush is just barely coated. Pounce here and there, but covering less than you did with the silver layer.TIP: You can use just one brush for this finish. Wash out the brush between paints and squeeze dry with a paper towel before using on the next color. It’s okay for the brush to be damp, since we are doing a blotting/dry brush technique here.
White layer. Repeat the process with the white paint for the highlights, except: after pouncing a section, use a rag or paper towel to wipe and smear the white paint as it dries to create a mottled look. Push the paint into the crevices to replicate a weathered look.
Metallic silver layer #2. Finish your fake galvanized piece with a last layer of silver. This time, really remove most of the silver paint from the brush by blotting on a paper towel. Lightly drag the brush over all the other layers, using the rag as needed to blend and give a smoother finish.The photo above shows what you’re after – the silver layered house on the left has a smoother, more galvanized finish than the one on the right. You can see how all those layers work to create the different lights in the finish though, can’t you?As an option to protect your finish, you can spray all over the item with a clear coat finishing spray paint in a satin or eggshell finish. You want to avoid anything glossy, since that is not a feature of galvanized metal.