Humbrol ENAMEL Thinners 125ml. Reduce the density of Humbrol Enamel paints, commonly used when applying Humbrol Enamels via an Airbrush. Thinners is available in small and large bottles. Usage: Thinning down of solvent-based enamel paints, most commonly for airbrushing. Application: As for the paint being used. Drying Time: Paint drying times may vary with the addition of Enamel Thinners.