I used to ponder this same question when I got into modelling. There are several techniques for weathering panel lines. Some use thinned artist oils, thinned enamels and most popular is the "sluge wash" using acrylics intoduced by FSM Senior Editor Paul Boyer. The later is very easy, forgiving if you make a mistake and every color in the rainbow is available in acrylics. The basic tecnique is to mix acrylic paint with water and add a generous portion of dish-washing detergent to create a thick sluge. Stirr the mix well, don't shake..it cuses alot of sudds! The key to the sluge wash technique is to make sure that the surface of the model is glossy. Most modelers airbrush Future floor polish as a gloss coat on the model before applying the wash but I like to use Testors gloss Laquer because It crues much faster than Future and I can go emmediatly to applying the wash. With a #0 round paint brush I paint the wash into panel lines, wheel wells, landing gear, cockpit interiors, etc. One of the the benifits of the sludge wash is that it's thick viscosity helps the wash stay where you put it. Now let the wash dry for approx 20-30 min. You can even speed things up by using a hair drier set on low to help the wash dry within 2-5 min. To remove the eccess you can use Q-tips, a moist paper towel, or old T-shirt scraps. Wipe the washed areas of the fuselage in the direction of the airflow; from front to back. For the landing gear and wheel wells wipe in the direction of gravity; from top to bottom. Another benifitt is if you miss a spot or make a mistake, you can safely remove the wash with a wet paper towel. Warning: If your gloss coat is Future, don't use Windex for removal; it will strip Future as well! Testors laquer gloss coat is impervious to water. If you are satisfied with your results seal the wash with the appropriate flat or gloss coat. Some supplies I use for my washes:
1. Inexpensive artists-type tube acrylics (you can mix any concievable shade of color)
2. Testors clear gloss laquer(base gloss coat protective barrier)
3. Distilled water (personal preference, tap will work fine)
4. Clear dish washing detergent (colorless types won't alter acrylic color)
5. Soft scrap cotton T-shirts, Q-tips, micro-brushes(for hard to reach areas)
Hope this helps take the mistery out of doing the famous "wash" technique. Refure to the complete feature article in FSM in reference Sluge Washes in resent back issues.
Happy modelling!
Greg Williams
Owner/ Manager
Modern Hobbies LLC
Indianapolis, IN.
IPMS #44084