What it measures: How thick or thin a liquid is; how easily it flows
Viscosity is a measure of a liquid’s resistance to flow. High viscosity = thick, slow-moving (honey). Low viscosity = thin, fast-moving (water). For airbrushing, getting paint viscosity right is foundational — it affects atomization, spray pattern, tip dry, clogging, and surface finish.
Target airbrush viscosity: Paint should flow like skim milk — thin enough to pass freely through the nozzle, but not so watery that it loses pigment concentration and adhesion.
Practical test: Stir paint and lift the stick. Properly thinned paint should flow off in a thin, continuous stream. If it drips in globs, it’s too thick. If it pours off instantly like water, it may be too thin.
Factors affecting viscosity:
- Paint type (lacquers are thinner than acrylics from the tube)
- Temperature (paint thins as it warms, thickens as it cools)
- Evaporation (paint thickens in the cup over a long session)
- Added reducer/thinner
Check viscosity mid-session and add a drop of reducer if the paint has thickened.
Related: Reducer · Flow Improver · Atomization · Spider Webbing · Orange Peel