The razor blade is good for an experienced guy but would be too easy to drag an edge and have to repaint. I would suggest 600 wet on a 1X2 short board (Wood) also a short piece of wooden paint stick will work lots of soapy water and keep board at the diagonal light pressure and sand useing stroke that follow the line if the run. Every few strokes check run. As soon as it looks flat change to 1200 wet just enough to get rid of the 600 scratches. Then buff. Remember light touch and take your time and make sure paint has cured.