Reducing Viscosity: Acrylic and Lacquer Paint
Solvent-to-Paint Ratio
Countering the Vague Dairy Reference
Social media abounds with decision fatigue when making up one’s mind as to properly thin paint for the perfect airbrush ratio. Often a vague reference is made about thinning paint to the consistency of milk or topping up the new glass bottle of paint with thinner.
What Works for One Doesn’t Work for Another – The Variables:
- airbrush type
- nozzle design
- spray pattern
- needle size
- air pressure
- air compressor type; with or w/o air tank
- airflow volume
- MAC Valve
- paint viscosity
- thinner type
- thinner/paint measurement
- paint age
- paint type
- paint pigment
- paint quality
- how well the colour is thoroughly mixed
- pre-thinned airbrush ready
- single action
- double action
- trigger control and/or double-actioning discipline
- experience
- airbrush proficiency
Airbrushing Styles
There are two airbrushing styles, to lay down coats of paint or fine detail, artistic approaches. Each approach has its advantages and disadvantages when it comes to thinning paint.
The Goldilocks Zone: 50 – 80% Thinner to Paint Ratio
Dialling in the ideal thinner-to-paint ratio requires consistency of measurement, as opposed to rolling the dice and guesstimating the outcome.
We are dealing in drops—20 drops per millilitre (0.05 ml per drop)—when it comes to modelling volumes, not litres. The size of the drop is not important, the consistent count is. Count the paint and thinner drops.
Most airbrush paint cup capacities are 7 mL or 140 drops to spillage capacity. Typically, the paint cup is about ½ to ¾ full, depending on whether back bubbling is used for mixing.
Air Pressure Regulator – Set it Once
While depressing the airbrush trigger for airflow, about halfway, adjust the regulator to 1.5 bar or 21 psi and leave it there.
It may read more pressure when the airbrush trigger is off, but when resuming airbrush operation, the compressor should operate at the defined setting.
Dialling in the Thinner to Paint Ratio
Here is where measured volumes convert to consistent paint application.
We need to get a data point to work from, so a 1:1 thinner-to-paint ratio is best to start with.
Increase the amount of thinner for the desired consistency, using styrene test cards with notations kept for future reference. Conversely, if more paint is required, add a drop at a time. Test with each graduated step. Season to taste.
Styrene Test Card
Make several 3 in (72 mm) square test cards from a sheet of Evergreen-type bulk styrene sheets for test spraying your favourite paint.
Styrene is superior to absorbent paper towels or sheets of paper for assessing thinning and spray pattern characteristics because it has a slippery, nonabsorbent, smooth surface, replicating the actual model about to be painted.
It’s All About Data Points
- When the air compressor delivers consistent airflow at a predefined pressure, the air coming out of the nozzle is a known data point.
- The measured thinner-to-paint ratio is the 2nd data point.
- Confirming how the paint is flowing on the styrene test card is the 3rd data point.
- Making any adjustments and retesting is the 4th data point.
- Making a note on the styrene test card for future reference is the 5th data point.
- Testing the paint ratios on styrene test cards develops airbrush trigger control muscle memory for consistent airbrushing results, the 6th data point.
- Being mindful of the airflow and how much trigger pull for paint is required—muscle memory development—the 7th data point.
- The spray pattern, overlap, and nozzle distance from the surface is the 8th data point.
Airbrushing Consistency
Armed with 8 data points, we now have paint mastery in our hands. If the paint results are not as expected, examine the data points to see where the process went off the rails. 
