Practical advice for scale model builders
When airbrushing with multiple colors, use a 0.5mm nozzle and set the airbrush to 15-20 PSI. Load the airbrush with a small amount of paint, and then mix the colors by adjusting the air pressure and the amount of paint in the cup. This will allow for smooth transitions between colors and prevent over-spraying.
When hand painting small details, use a 00 or 0 brush and thin the paint with a medium such as water or Vallejo's Flow Agent. This will allow for smooth, even strokes and prevent the paint from pooling in small areas.
Use a primer specifically designed for the type of surface you're painting, such as a plastic primer for injection-molded plastics or a metal primer for aluminum or steel. Apply the primer according to the manufacturer's instructions, usually 2-3 thin coats spaced 10-15 minutes apart.
Apply decals to a surface that has been primed and painted, but not yet topcoated. Use a decal setting solution to ensure the decals adhere properly, and then apply a thin coat of varnish or gloss to seal the decals in place.
Mix a wash by adding a small amount of water to a medium such as thinned paint or wash medium. Apply the wash to recessed areas of the model using a small brush, working from dark to light. Use a soft cloth or brush to remove excess wash from raised areas, blending the wash into the surrounding paint.