It's going to depend on what you painted it with. I paint with enamels, and I like to use water soluable artists oil paints. A lot of guys paint with acrylics and use either an enamel wash, or an artist's oil paint wash. Several guys use inks as well, though I've never done that myself. I've heard and seen good things about all of these methods.
The bottom line is that you should probably try several different methods on some scrap, or other less noticeable pieces of the plane, and find what suits you best. You'll get the best results with a technique you're comfortable with and have developed confidence in. Practice makes perfect, trifles make perfection, but perfection is no trifle.
Madda
Trifles make perfection, but perfection is no trifle. -- Leonardo Da Vinci
Tact is for those who lack the wit for sarcasm.--maddafinga