Squeeze a less-than-dime-sized portion of black paint onto your palette. Do the same with blue.
Dip your paint brush into the jar of water.
Allow several drops of water from your paintbrush to form a small pool in the center of your palette.
Dip the tip of your paintbrush in the black paint.
Dip the paint brush into the pool of water. Swish the brush around.
Dip the tip of your paintbrush in the blue paint. Pick up a minuscule amount of blue paint.
Swish the tiny, minuscule amount of blue paint in the pool of black-ish water in the center of the palette.
Test the color you've created on a strip of test paper. It should look silver-gray.
Adjust the color as necessary, adding black and blue, or adding water as needed.
Apply the paint to the paper one layer at a time. Paint around the spots where the sun or light is focused on the metal object. Apply the paint in layers receding from the paint-free, bright spot.