I don't paint blades for other people anymore simply because it is going to chip no matter what. I do use powder and I have done just one side and I've done both sides and there are some things to consider. If you have plain brass blades, you have to make sure they aren't lacquer coated, if they are then soak overnight in mineral spirits and then wipe, rinse and dry before painting. If you are going to do one side you need to put a top coat on both sides or the unpainted side will tarnish or rust if using raw steel blades. I normally use Devcon 2-Ton epoxy for all my top coat needs but it adds too much weight to a spinner blade so I like to use the Component Systems Seal Coat, you can use it on powder or create. Before you paint I recommend roughing the blade with fine grit sand paper, I like 3M 400 grit wet/dry, a few passes will be enough to provide a surface the paint will adhere to without making it so rough that the paint will end up with a texture.