Although it may not truly affect anything, a raised transition line between colours on a new paint job can ruin the overall appearance of a custom car or truck. These lines or ridges are created as a second layer of paint gathers and dries at the edge of a masked-off area. When the masking tape is removed, the transition line remains.
Clean the area around the transition line with denatured alcohol and a lift-free towel to remove any dirt or dust from the surface. Allow the surface to air dry for at least ten minutes.
Place a sheet of 1000 grit sandpaper on a foam sanding pad. Saturate the sandpaper with clean water. Using gentle pressure, sand along the transition line while moving in a single direction. Stop occasionally to clean the sanded area with water applied from a spray bottle. Continue sanding until the transition line has subsided, progressing between 1500 and 2000 grit sandpaper to remove sanding marks.
Apply a small amount of buffing compound onto the sanded area. Buff the area lightly with an electric hand buffer to remove any remaining sanding marks and to restore the paint's lustre.
To avoid creating swirls in the paint, use a side to side motion instead of a circular motion while sanding.
Do not sand the painted area until you have removed all dirt or dust with denatured alcohol. Debris on the surface can become trapped in the sandpaper and damage the painted area.