Many believe that graphite lubricants are a commodity product. In other words, all rattle/paint cans of graphite coatings are all the same. In reality, there are two main things that govern the performance of the graphite lubricant that you purchase – amount of graphite and the type of graphite.
Graphite is much more than just what is in your pencil. It is mined and can be extremely expensive depending on the type of graphite and its purity. For example, vein and flake type graphites are the most lubricious grades compared to amorphous and synthetic graphites.
Another factor that governs graphite coating performance is the type and amount of binder. The binder is the glue that allows the graphite to stick to the surface and to itself. Finding the right balance is important as it could mean poor performance. Too little binder would simply allow the graphite to blow off allowing rust to occur where too much binder might hinder the lubricity.
There are several tests that laboratories use to evaluate the performance characteristics of graphitic coatings. The choice of graphite materials with its coating formulation will dictate the effectiveness and long-lasting nature of the lubricant. A water resistance test looks at signs of rust corrosion after three days. A crosshatch adhesion test looks at the strength of the graphite coating material sticking to a metal surface. The water and solvent rub tests evaluate the durability of the graphite coating before bare metal is visible. Lastly, a friction test under a heavy load of friction determines the slipperiness of the material before the material is worn and the coating fails. The best graphite powder dry lubricant would be the one with the highest marks in these tests and therefore would imply how well it would work in your application.