Newbie Q's on priming, paint amount

Priming in scale modeling has three functions:

1. finding flaws in the surface—use a light color.
2. backing up a translucent color like white, yellow, red, or orange. For white, prime with silver, for yellow, red, and orange, prime with flat white. Flat paints have better hide than gloss paints.
3. improving adhesion (bond) of the finish color to the surface. In scale modeling, this should be unnecessary since most of the surfaces are nonporous and should be clean.
   

Primer color should usually be a light one, preferably a very light gray. Do not use automotive primers, as they are intended to be sanded and produce such a thick coating that detail will be covered.

Thin only slightly more paint than you think you will need to cover the intended surface. You can always thin (reduce) more if you need it. You can store most reduced paint for several days to a week without adverse effects, provided you used a completely compatible solvent. However, paints are formulated to be stable with a certain proportion of solvents. Changing that proportion can, and often does, reduce their long term stability.