When the early to mid 1980's saw the introduction of specialist detail parts designed to complement existing kits, modellers found themselves with a range of parts that previously would have to have been scratch-built. This trend was partly encouraged by early vac-form kits in the late 1970's which had small parts vacuum formed as well. The technique does not lend itself well to the production of parts such as propellers and oleo legs, hence the introduction of cast white metal parts. The advent of photo-etched metal sheet, and then cast resin components, opened the detail part range up to involve injection moulded kits as well; Verlinden being a major contributor to this new direction. It was the introduction of cast resin, with its inherent precision and fine detail, that has allowed the after-market detail part industry to take off. The application of chemical photo-etching technology, introduced by companies like Model Technologies and Foto-Cut, finally gave the modeller the kind of precision they had been looking for and allowed parts to be made that were previously impractical. With the introduction of photo-etching, emphasis was initially placed on creating generic detail sets for the modeller. As the popularity of photo-etching rose, emphasis swung towards component sets designed for specific types of aircraft as we see today. The Census here lists known generic sets and components; detail parts specific to an aircraft type are listed elsewhere under that type.