Camouflaging a model kit happens in the final stages of the build up and it can be very rewarding. There are ways to get a hard edge camouflage pattern by using masking tape, masking paper or liquid masks that might be suitable, for example, for modern combat aircraft. However, since camouflage on armour and aeroplanes has often been created freehand by soldiers with spray guns, the soft camo look is typically preferable and can be attained using stiff paper or freehand techniques.
A mask on a model kit simply refers to any kind of material that blocks the flow of paint from getting to the surface of the model. Traditionally, modelers have used masking tape although it can be too sticky and leave tack behind. You can also use painter's tape, which is typically blue or green, and trim it to your liking. There are also liquid latex masks that brush on and can be pulled off the surface of a model. Finally, some modelers like masking paper, which can be cut or even printed on to get the right shape for a harder edge.
Paper Template Soft Edge Camouflage
If you are inclined to use a template, or series of templates, you can cut your camouflage pattern from stiff paper. Cut the curves or shapes you want and lay them over the base coat to protect the dominant colour, which should be the lightest colour. Then, spray the area around the paper to create lines and shapes. Repeat this process, covering your work as you go, to get a camo pattern. The paper will allow a bit of paint to come in from the sides, which will leave a soft edge.
Freehand Soft Edge Camouflage
Using an adjustable or dual action airbrush operating at an air pressure of between 20-25 psi, spray on the base -- or dominant -- colour, which, again, should be the lightest colour. Reduce the air pressure to about 15 psi and use a reference pattern as a guide to spray on additional colours. Air pressure may have to be adjusted to accommodate different humidity, barometric pressure and paint consistencies but basically, the goal is to get an even flow with a controllable spray. The closer your airbrush is to the surface, the more defined the lines will be.
If you are painting subjects from nature, such as wild animals or dinosaurs, your paint application should be soft because a military style camo will not look right. To achieve a more natural flesh or fur look, layer transparent paints over a natural base tone, such as tan, green or grey. When the paint is dry, seal it with a dull coat sealer. Then mix one part black or brown oil paint with 19 parts paint thinner and brush over the entire surface. Wipe clean to leave a natural finish.