People who have seen early attempts at 3-D modelling remember how neat, clean and artificial many early 3-D models looked. Early computer models captured the shape, accurate proportions, and often the general colour of an object, but not the fine details, and certainly not the imperfections. We minds intuitively sensed there was something not right.
The models earlier generations used for films were prone to the same drawback. They needed some fine detail and ‘grit’ to look realistic. Often this could be covered up with by the lower resolution of the picture, with a slightly ‘dirty’ looking model passing a casual glance. But the same principle still applied- the model couldn’t look like an architect’s diagram.
A process called ‘greebleing’ was developed for many film models of the 1970s. This was just the process of adding details to surfaces to prevent spaceships in Star Wars from looking like simple geometric shapes. The added details served no real function other than adding to the realism of the object. Our minds expect this. Real objects have both overall shapes and minor details. Models must replicate this on a very small scale.
Plastic model decals add to the detail of their respective models. In isolation the decals are often quite simple – emblems, shapes, insignia or just isolated words. But when these simple decals are added to a larger object they are part of the accumulating detail. None of the details are complex on their own, it is the large number of simple details that give the overall impression or complexity, and hence, realism.
Custom decals will be made to a specific design, such as the insignia of a military vehicle or the personal logo of the creator. All the other applied details are less specific, but the overall effect creates a model that is far more convincing.