humbrol satin cote question

To thin, use either Humbrol thinner, or general purpose enamel thinner from an automotive paint / parts store.

Ratio - thin to preferred consistency. For brushing, a new tin needs no thinning. For spray, thin to fluidity required for that nozzle / pressure combination. It can be hand brushed - use a flat profile, soft sable brush.

Airbrushing is also OK, thin to correct fluidity (the commmonly touted rule online appears to be 'the consistency of milk', but what kind? Full cream, low fat, reduced fat, half fat, soy, added calcium......???) Clean the airbrush with thinner afterward.