Whenever you've asked the question, "How much should I thin my paint before airbrushing?", how often have you heard the recommendation that you should thin it to about the "consistency of milk"? Just what does that mean? Well, if you're a buttermilk drinker, you better keep reading or you're in trouble!

MIXING FOR PROPER PERFORMANCE

Before you do any actual mixing, take some time to think about what you're mixing. Lacquer materials are complex formulations of any number or type of chemicals. No two are exactly alike. That is, brand X lacquer and brand Y lacquer may both be named the same and used for the same purposes but they are not the same formulas. They may be compatible with each other or they may not.

Imagine you've just bought a jar of brand X lacquer paint. Well, brand X lacquer thinner is recommended for use with it but you happen to see brand Y lacquer thinner at the local hardware store that costs a few dollars less. You take it home, combine the two, apply it to your model, then discover when you're done there's some unusual "bubbling" happening on the finish, or the paint didn't cover evenly, or it's crinkling and cracking while drying. After you've learned the hard way that brand X and brand Y products don't work well with each other, what do you have? Wasted time and effort, a jar of useless paint, and possibly a ruined model.....but at least you have a few extra dollars in your pocket, right? Was it worth it?

This is good advice for any paint you work with whether it's automotive, hobby, or even house paint for that matter. They're all complex chemical formulas scientifically designed by manufacturers to intermix with that manufacturers own specific products. You wouldn't try jamming a Ford camshaft into a Chevrolet engine just because it was cheaper to fix your car that way. Don't try it with paint either. Ford doesn't engineer parts for Chevrolet. Paint companies are no different. Experimenting may work or it may end up costing you in the long run. Choose your products wisely.

MIXING FOR PROPER CONSISTENCY

It may be more useful to understand the habits of primers and paints if you think of them in terms of not being so much a liquid as they are an assembled collection of unstabilized components. Shifting, settling, and evaporation are actions that are always occurring at some level which affect the quality of results. These are factors which must be kept in consideration both before and during applications.

Before you begin to airbrush a primer or paint it's a good idea to check your mixture for lumps, settling, seeding, or contamination that may inhibit it from being a smooth blend. Glass containers afford you the ability to visually check if a mixture is completely mixed after shaking it up to agitate any components that have settled. With other containers such as cans you can shake the mixture up, but it's a good idea to also stir it with a stirring stick so that the bottom of the container can be scraped to check for unmixed settled components. Unless a paint or primer has been sitting unused for a very long period of time shaking it should mix it thoroughly for proper use. If you stir a mixture and find that you've dislodged settled components you may want to filter the mix through a strainer before you use it to avoid consistency problems when it comes time to airbrush.

One more thing to keep in mind - if you transfer materials from one container to another make sure the new container is thoroughly clean and dust free. Any contaminants that get into your mixture will be nearly impossible to detect until it has been applied to a surface. It's a lot less work to clean a jar or airbrush color cup before you spray than it is to remove dirt from a painted surface afterward.

THINNING PRIMER

The proper level to thin your primer is best judged by signs exhibited while airbrushing. Primer is also a bit more susceptible to change over a period of time than lacquer is, especially when it comes to evaporation. Check your mix every time you spray your primer. Even leaving the lid off your primer container for too long during a single application session can cause enough solvent evaporation to make your perfect mix soon become too thick to effectively spray.

There are two main things you should look for if the primer is too thick:

First, check for build up around your airbrush nozzle when spraying. If this is happening it's because the primer is sticking to the needle and tip causing the spray to be erratic. Not only will the spray itself be blotchy when it hits the surface of your subject but the build up will also be at risk to be sucked into the airflow stream and onto your surface in larger spots, making the application coarser. This is not the worst thing that can happen, but it creates extra work later to sand it smooth and can help obscure details on the surface you're spraying.

Second, watch to see how the primer is flowing out as it is applied to your subject. Primer does not have quite the same flow characteristics of lacquer but it still flows during moderate to heavy coat applications. If it is too thick you will see the surface developing an orange peel texture similar to that of lacquer. Again, this will mean more work to sand it smooth later.

 It's better to have primer too thin rather than too thick. Primer thinned too much sprayed on too heavily will increase the likelihood for runs or sags to develop, and you will need to apply more coats to get good coverage, but with a little extra patience a thinner mix will get the job done more effectively than if you try to force a thick mixture to work. Adjust your mix to find the proper balance between thick and thin and you'll enjoy the best advantage offered.

THINNING LACQUER

The popular "consistency of milk" statement is an interpretive reference that really isn't based on any specific ratios or formulas for mixing. This is a way of relating in common terms the average viscosity of a paint that's suitable for airbrushing. Not quite as liquid as water, but not as thick as syrup either. Laying out a specific mixing ratio is next to useless. Even if you could, a good ratio for your paint might be OK today, but the same ratio for the same paint a month from now might not be OK. The qualities of the paint may have changed due to evaporation or chemical reaction. Each time you thin a paint you have to adjust to the paint's current condition.

Now then, as a general rule of thumb only, most automotive lacquers are formulated to be thinned on a 1:1 ratio with thinner. This is a good starting point but should be considered only that. Once again, going on from this basic point of reference, learning how to "feel" what the right mix for a paint is can be better judged by signs observed while actually airbrushing.

The classic sign that your lacquer is too thick for airbrushing is "veiling". While you're spraying you will notice that the paint is drying before it hits the surface of your subject and will begin to form a cobweb or cotton candy-like texture. When you see this, stop immediately and add more thinner to the lacquer. Continued spraying of additional coats over the cobweb material will only add to what's already there as well as harden it.

You might think that adding thinner will cause the mixture solvents to evaporate more quickly and make the problem even worse. On the contrary. Unthinned lacquer generally dries faster than thinner. Lacquer thinner serves two purposes:

	Increases the viscosity of paint to allow it to be airbrushed.
	Slows the drying time of the paint mixture to increase flow.

Thinners are available in varying degrees of drying times that, when combined with the air temperature of the environment you're working in, greatly affect the evaporation and flow qualities of your paint. For hobby purposes, the slowest drying thinner is recommended for airbrush use at all times.

As with primer, paint that has too much thinner added is not ideal but is better than being too thick. If your paint is too thin you will have to apply more coats to achieve good color coverage. You also risk the greater likelihood of runs and sags developing during moderate to heavy coat applications so always be on guard for this. Patience will yield good results.

In time you'll be able to judge how thin a paint needs to be for optimal airbrushing simply by looking at how thick your paint is before and after you thin it. In the mean time, relax and enjoy a glass of milk!