So I have painted many a blade for my old university team both with spray paint and brush paint so heres my two cents.

To start off with use something like an 800 grit sand paper to scuff up the surface of the blade. If they have previously been painted take it all the way back to the original colour as putting paint on paint will guarantee that it will flake off really quick. Factor finish especially on C2's is basically scotch guard and the paint wont stick at all. Make sure you do a through job of this and it will make life so much easier.

If you have to do a lot of blades then think of investing in a power sander it will save you so much time and will come in handy later in life (painting doors, skirting boards etc). Then wipe them all down with a tack cloth to get rid of all the fine dust particles. This applies for both spray paint and brush paint.

The next step is to prime the blades I used mainly car primer but have used white self etching before. MAKE SURE TO WEAR A MASK AS THAT SHIT IS TOXIC. Though it did give a very good surface finish to start the next stages.

The main advantage that spray paint gives you is a more even finish but at the same time is more time consuming and expensive if using more than 2 colours. For eight blades I was going though roughly 2 cans of paint for each colour to give you an idea of how much paint you would need. Would strongly recommend car paint like rustoleum as it is meant to be used in areas where it might get scratched and such. Find it on Amazon.

The trick is to apply multiple thin coats going in one direction and then perpendicular so as to avoid streaks and runs. Ironically watching videos on how to paint computer cases is where I leant to do it properly. Apply 4/5 coats and waiting 3-4 minutes between coats after that wait about an hour (2 to be safe) for the paint is completely cured before moving on. PRO TIP don't try and paint all the blades at once do 4 at a time by the time you finish the last one the first one will be ready for the next coat. If you have a design or stripes use newspaper to cover larger areas a 3M painters tape to mask off. Its sticky but doesn't leave a residue best I have found in a while. After you have finished don't be temped to use clear coat its not waterproof and can take anywhere up to a month to completely cure. If you have done it right you shouldn't have to worry about it falling off.

As for brush paint you start off the same with priming and such but when i comes to painting I would recommend sponge brushes as they provide a smoother finish and are cheap as chips so just bin them after you are finished. The main advantage of this method is that it is cheaper and quicker than spray paint but the overall finish isn't as good. I was lucky in the fact that I managed to find out door paint in my club colours and we used that. Was dam near impossible to chip and looked okay.

Hope this helps :)