The most important finish of a fabric covered airplane is the sprayed on silver finish. These multiple coats of silver are basically aluminum particles suspended in the vinyl chemistry to protect the fabric from the harmful effects of the Sun. There is usually a minimum of three coats of the Poly Spray material needed to bury the fabric in metal. A work light is placed behind the fabric to inspect if enough silver has been applied to totally eliminate any light penetration through the fabric. The silver/fabric material is carefully sanded with 320 / 400 grit sandpaper between coats.
The next spray coats will be a White Poly Tone Color that is used as a base finish prior to spraying the final classic 146 J3 Yellow. The White is needed to cancel the gray tone of the silver otherwise the Yellow color would be a greenish and hideous color.