This is an article that I wrote (using various references) for my modeling club newsletter last month. It may not answer all your questions, but it may help.
"This month's tip concerns paint. A simple subject, but one that still baffles modelers. Paint is manufactured using complex formulas that are constantly being modified and improved.
What is paint?
Generally speaking, all paint is made up of three components: a pigment, a vehicle, and a solvent.
Pigment is the material that gives paint its color. Pigments can be organic or chemical, but pigments have nothing to do with how the paint is classified.
A paint vehicle is material that bonds to pigment and remains on the surface once the paint dries. The vehicle is what gives paint its protective properties.
A solvent is any liquid that dissolves the vehicle to make paint liquid in the bottle or can. Note that a solvent does not have to be a chemical. Water is a solvent if it dissolves the vehicle in a given paint.
How are paints classified?
There are only two general classifications of paint: enamels or lacquers.
Enamel paint is one that both dries and cures once applied to a surface. As the solvent evaporates, the vehicle undergoes a chemical reaction making it harder and less soluble than the liquid paint. This is why you typically can't remove fully cured enamel with the same solvent as in the original paint.
Lacquer only dries – it does not cure. The solvent evaporates with no chemical reaction. This is why water-based lacquers can be dissolved with water long after the paint has dried. This is also why applying multiple layers of lacquer can result in the underlying layers dissolving.
What about Acrylics?
"Acrylic" refers to the vehicle used in paint and not with how the paint reacts once it is applied. The vehicle in acrylic paint is a form of plastic and there are both "acrylic enamels" and "acrylic lacquers". There are also both petroleum-based and water-based solvents for each of these acrylics, depending on the vehicle formulation.
For years, modelers, hobby shop owners, and even "experts", have referred to modeling paints as either enamel/lacquer (meaning that the paint uses a chemical solvent) or acrylic (meaning that water is the solvent). This is just plain wrong and only adds to the confusion. Try adding water to a petroleum-based acrylic enamel and you quickly realize that not all acrylics are water-based. Water-based acrylics should be referred to as "aqueous acrylics".
What are the differences in paints?
Traditionally, enamels have used a relatively mild petroleum-based solvent with an alkyd vehicle. This combination, while generally safe, takes a long time to cure, sometimes weeks to reach maximum hardness. They are an extremely stable paint and can last for decades without degrading, if properly stored. There are now enamels that dry nearly as fast as lacquers and nearly as hard.
Lacquers tend to dry quicker and to a harder consistency than enamels – typically in 24 to 48 hours. However, they use harsher solvents to accelerate the drying time. These solvents can attack plastic parts, brush bristles, and brain cells with equal vigor. There are now lacquers available that use much milder solvents (including water) yet maintain their traditional hard finish.
With the advent of aqueous acrylics, many of the differences between traditional paints have merged, but aqueous paint has its own problems. Some people think aqueous paint doesn't "stick" to styrene parts like chemical paint. Aqueous paint is more sensitive to humidity and temperature. Modelers who choose aqueous acrylic paint generally do so to avoid exposure to chemicals.
So what's the best paint for me?
This is the ultimate question and one that each modeler must answer them self. There are distinct advantages and disadvantages between paints and manufacturers. Each modeler must evaluate the good and bad points and make their own choice.
It appears as though aqueous acrylic lacquers and petroleum-based acrylic enamels are two types of paint that are becoming the waves of the future.
Aqueous acrylic lacquers take the best properties of enamels and lacquers and combine them into a nice package. Although they don't dry as quickly or as hard as "traditional" lacquer, they are getting better. As environmental concerns grow, these paints may be the only option available a few years.
Petroleum-based acrylic enamels are modified versions of the same enamels modelers have used since the 1960's. Because they use an acrylic vehicle, these paints dry faster and harder, but they use a slightly harsher solvent than older enamels.
I hope that this article clears up the subject of paint (at least a little bit) and helps you decide which paint is right for you. Next month we'll continue with paint and cover some tips and tricks for storing and using paint more effectively."
Enjoy your modeling...