This paper presents the true three-colour photoceramic, introduced by the authors since 1992, which allows wide new possibilities in the field of the ceramic decoration, for reproduction on ceramic (majolica, porcelain, earthenware, etc.) surfaces of images either photographic or painted images or even directly coming from computer-made image files. The correspondent technological process used to produce this kind of decoration involves new manufacturing procedures and the use of unusual devices. The physical principle involved in obtaining the formation of the image is based on the well-known physiological tristimulus effect, which is founded on a consolidated theory and practice utilised for classical photographic and TV reproduction. The novelty consists in having introduced this technique in the ceramic decoration field. To distinguish the technique described here from that already known as polychromatic, based on a careful and artistic hand-painting technique (but an artefact based on the operator's fantasy), we have called it: true three-colour photoceramic process (the equivalent of the three-colour printing technique). Besides the due treatment of already known physical concepts, some technological problems are reported and discussed, which arose during the years of utilisation of this new technique. The behaviour "in situ" of true three-coloured photoceramics is also discussed here, in the light of many years of production and application. Physical and chemical aspects are considered, to further develop and improve this new technology of images reproduction.