The models of spaceships and vehicles in early Sci-Fi and fantasy films (think 1936’s Flash Gordon) had their limitations partially covered up by the poor picture resolution of the time. Later films had better resolution, so models needed to look more convincing. This required some unexpected efforts on the part of model builders.
Neat, clean models of vehicles look unconvincing on film, because we sense that real vehicles have fine detail and ‘grit’. Adding some of this detail and grit became common practice in 1970s films. The term and practice of ‘Greebeling’ started with the first instalment Star Wars; Director George Lucas insisted that the aesthetic was to be a ‘used future’. Spaceships and robots were covered in a maze intricate raised details, and the result looked far more realistic on film.
Early 3-D computer modelling suffered the same fate as early film models. Early computer models captured the shape, accurate proportions, and often a reasonably accurate colour for an object, but not the fine details, and certainly not the imperfections. Our minds intuitively sensed there was something not right. The adding of details, the greebeling, became necessary before 3D models began to look realistic.
Real world objects have both overall shapes and minor details. Models must replicate this on a very small scale. Adding these details to a model is a combination of 3D and 2D details. Waterslide decals are an excellent, if obvious, choice for lettering, symbols, insignia, emblems, coats-of-arms and many other 2D details. They can also be a good choice for providing shadow and the illusion of 3d detail. In isolation the model decals are often quite simple, 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