In model building, it is usually necessary to apply a gloss coat before applying the decals. Many different brands of gloss coat are available in the hobby shops. Future floor wax is also very popular as a gloss coat. The gloss coat prevents the decals from silvering. Silvering is the term for the ugly result that happens when a decal with the clear film is applied to most flat surfaces.

In use a mix of 1 part future to 1 part water at 30 psi (to get a fine mist). Spray on a fine coat and let dry for about 30 minutes then put on another coat. Do this as many times as is needed. Do not put it on too thick at once or it will run. I recommend flushing out your air brush between each coat with water so the polish will not build up.