This is probably the most enjoyable aspect of creating a realistic looking model aircraft kit. In most cases, this scale modeling technique is procedural and the results are fantastic.
In order for your decals to look like they have been painted on, it is important that they be applied to a glossy surface. To prepare the surface, you can purchase Future Floor Wax and airbrush it directly on top of your paint scheme. There is no thinning required. Simply spray it onto the model aircraft kit as is. Be sure to apply a very thin coat and use a low PSI of 15-20 lbs. on your air compressor. It may look messy going on, but in about 1 hour, it should dry to a shiny, tough surface. The resulting surface will accept the decals very well. Clean your airbrush and tips after this step using either warm or hot water.
For organized scale modeling, I prefer to separate stencils, insignias and personal markings using a pair of scissors or a modeling knife.
Dip your decal in water for about 10 seconds and place it on a non-absorbent surface until it loosens from the backing. When the decal is loose, place it with the backing next to the desired location on your plastic model airplane. With a damp finger, slide the decal onto the model aircraft kit and pull the backing paper away while letting the decal drop to the surface. Once the decal is in place, you may want to use a damp cloth to lightly tap away some of the excess water.
Using a brush, apply a setting solution – such as Solvaset – over the decals while they are still moist. Then, allow 24 hours for the decals to dry and adhere to the plastic model airplane. The setting solution should soften the decal film so that it stretches over the surface details, such as rivets, and improve adhesion without damaging it. After this drying period, wipe away the excess solution with a moist cotton rag.
At this point you can seal the model aircraft kit with either a flat, semi-gloss or glossy varnish prior to weathering. It’s the final clear coat that seals the decals and makes them appear like natural paint.
If this is your first time attempting this technique, I highly recommend that you practice using spare parts and decals before applying it to your built plastic model airplane. Enjoy the scale modeling technique.