hi swfong!
Pre-shading is a way to deepen panel lines, creating a 'worn' look. If you look at an F-14 Tomcat you'll notice that the lines are a little darker than the center of the panel. This is what we modelers are trying to duplicate. If you have an airbrush and can tighten the pattern than that is the way I recommend applying it. All you do is to take the base color (dark grey, etc.) and spray the panel lines. Then you follow up with the lighter color and spray between the lines. I don't use black simply because that means you would have to airbrush the whole model the lighter shade, maybe more than once, to cover the black. I spray the model with the darker base color and then spray in between the panel lines with the lighter shade. This gives it a patchy, replaced look. It looks great on Modern Naval Aircraft, like the F-14, F-18, and the F-16 as well. I also preshade the lines on my WW2 as well.
I use the airbrush simply because it doesn't over load the paint in the panel lines like a brush can sometimes do. I have heard of people using a black magic marker to preshade but I have yet to see one like that. Practice, practice, and practice on an old model and you'll soon love how realistic it can make a model appear. It really adds a nice weathering look to it.
There also is post-shading as well, and that is re-applying a lightened or darkened version of the same color over itself. Essentially highlighting or darkening the lines. One step at a time eh?
I hope this helps and I haven't confused you! If you would like some reference check out this site: http://www.naritafamily.com/howto/F14D/photo_frame.htm
-scroll down the left side of the site until you find the 'painting' part. Massa has mastered the art of preshading and has some stunning builds there along with some pointers into weathering etc.
Have fun!
Regards,
Jon
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