Thinning

The basics of using the airbrush starts with proper paint thinning. But thinning in itself is difficult to teach through a website as there are just too many factors in affect. The same exact thinning ratio will work for a particular person, but for a different person will not work. The reason for this is the environmental factors that attribute to each person’s painting situation.

Painting in a high temperature and humid environment differs greatly from a low temperature, low humidity, and also high humidity and low temperature. Additionally, the exact viscosity of the same brand, color, and type of paint may be different to two people in the same area. One may have had more of the paint’s carrier evaporated than the other, basically a fresher batch of paint verses a old batch of paint. Add in the different airbrushes and different pressures we all paint at; it’s impossible to get an exact thinning formula that would be the universal standard.

So where do we start? A good starting point is 60% thinner to 40% paint. Then add more thinner or more paint accordingly. The more you paint and thin, this will become easier as you settle into your own paint groove. The key things to look at is the consistency. A good standard is the consistency of your run of the mill vitamin D milk. The truest test is to run a small sample of the thinned paint through the airbrush. If it’s too watery and a light misting of the paint is beading up as droplets – the paint is too thin. If the paint is having trouble exiting the airbrush, the paint is coming out in thick splatters, and the airbrush is making a fairly high pitched squeal because the paint is trying to squeeze out of the airbrush, the paint is too thick. I always have a sheet of paper or piece of cardboard in front of me to run a quick thinning ratio test before painting.

The general idea for paint thinning is that it is specific to each paint bottle and your environmental variables. A ratio that works for one paint bottle, may not necessarily work for another bottle of paint in your collection. Thinning is a skill that needs time and practice to become good and comfortable. So the more you build and paint, the better you will get with thinning.

Priming

Ok, enough with thinning; now that the subject is out of the way, we can get down to the real fun; spraying some paint. The first layer of paint I spray on a bare piece of plastic is always a primer. Primers come in gray, white, and black. There are some paint companies that make primers in all sorts of other colors. These are usually flat finish paints that are formulated to grip an unpainted surface. This helps prevent paint chipping. I spray primer first because it does several things:

Fills in small scratches from the sanding process
Shows surface defects that are still on the plastic such as missed nubs, missed seams, and poor sanding
Give a neutral color tone to start painting
Gives the plastic a very nice surface for paint to adhere

Small scratches that you can still see in the surface but cannot feel after you have sanding the part with a fairly high grit sanding tool will be filled in with the primer. Small surface defects that are difficult to see in an unpainted piece are clearly seen once the part has been primed. Most gunpla kits are precolored, so the primer neutralizes the colors so that the underlying colors do not tonally mess with the paint colors. For example, if you wanted to paint a black piece white, yellow, or red, the darkness of the originally black part will darken the tone of the paint. And lastly, primer helps paint stick to the surface. Giving the paint something to grab.

When painting (primer or paint colors) the first thing I do is spray a very light misting layer around the part. This acts as a buffer between the dry part and the paint. If I were to just spray on the paint, the surface is suddenly bombarded with paint and chances are, the paint won’t stick and will end up pooling. Below is a video that first describes the types of primers and uses, and demonstrates what happens when the paint pools.

From the above video, allowing the part to completely dry, the area can be sanded smooth and then repainted. See the following video.

Now for some actual color. And to avoid what happened in the above video, the paint is lightly misted around the part. Once this layer is done, you can spray on a slightly heavier layer, slowly building up the paint. Watch the video below.

Airbrushing is very similar to spray cans. Once the basics are practiced and mastered, we can move on to refining the airbrushing techniques.