RPM wax definitely blackens phosphated fasteners and small parts and makes them look much better than phosphated alone or phosphated and coated with grease or oil. Most hair driers should be capable of heating small parts enough to reach the melting point of about 120 degrees. For large parts you may need an oven.

You will want to make the hair drier operate hands free by propping it up somehow and holding the parts in front of it with pliers or similar. I swiped a wire stand from one of my flashlights, drilled two holes in the front end of the hair drier, and clamped the stand to my work table. A smaller 1" brush is better for small parts instead of the supplied 2-3" brush. Keeping the RPM container near the heated zone softens the wax and allows a heated brush to be coated. Like paint, you can brush off excess wax on the rim of the container.