Black nail polish has been useful in touch repairs of carbon frames, rim brakes and RD

 A P40.00 black hair nail polish has gone a long long way in making cosmetic touch ups of scratches and exposed bare metals of the following:

1.  Rear derailleurs

2.  Carbon frames

3.  Brakes

4.  Chain ring.   

You keep the bike still looking good.

The vid is its use on cars: