Opaque Base is the binder base for the 4200 Series Semi-Opaque Colors. Opaque Base may be added to color to increase opacity. Opaque Base may increase the viscosity of the color and is not recommended for use with smaller airbrushes and fine detail work. Opaque Base may be added up to 25% of the mixture, after that the colors tend to wash out as the pigment load is spread out. Opaque Base should not be used with Auto Air 4200 Series Detail Colors nor should it be used with 4300, 4400, 4500, and 4600 Auto Air Series.