http://www.revistadechimie.ro REV.CHIM.(Bucharest)♦70♦ No. 11 ♦2019 3860 The Photographic Sensitivity Mechanism - an Unlocked Subject VLADIMIR CONSTANTIN BACAREA 1 *, PETRUS FANEL BACAREA 2 , ANCA BACAREA 3 1 UMFST Targu Mures, Medical Scientific Research Methodology Department, 38 Gheorghe Marinescu Str., 540139, Targu Mures, Romania 2 S.C. Prochiral SRL, 66/16 Gheorghe Marinescu Str., Targu Mures, Romania 3 UMFST Targu Mures, Pathophysiology Department, 38 Gheorghe Marinescu Str., 540139, Targu Mures, Romania The paper aims to demonstrate how a dogma, favored by random experimental discoveries, can change the progress of research. It has been experimentally shown that photographic sensitization is achieved by adsorption of preformed sensitivity centers on AgX granules. The mechanism of classical sensitization can be the emulsion formation of centers concomitant with adsorption on granules. Key words: Photosensitivity, Sensitization center, Nanoparticle, Plasmon, Adsorption on the grain The present paper proposes an out- of-the-box approach to a phenomenon that is still unclear, the mechanism of photographic sensitivity. This subject, despite the impressive development of research, could not be resolved until the natural death of the classical photosensitive materials industry and the disappearance of the related interest and explosive market entry of the digital image. Classical photosensitive materials, based on silver halides and gelatin, have virtually held the image market (photography, cinema, printing industry, medical imaging, non-destructive control with penetrating radiation, recording and archiving of information, television, scientific research etc.) more than 150 years. The field of photosensitive materials has always been considered as a high technology and a very innovative one. Although it stretched over a very long period (more than 150 years) [1], no one can claim to have a complete and clear understanding of the process of image formation and preservation [2]. We try to explain this paradoxical situation not only by the complexity of the physics and chemistry of the process itself, but also by the counterproductive methodological approach of the study. We will point out a few crucial moments that marked the course of the research. The first purely experimental breakthrough was the use of gelatin for the incorporation of silver halide micro-particles. In addition to the exceptional qualities of protective colloid [3], which made gelatin irreplaceable until the end of classical photosensitive materials, it had a hidden active composition. Some amino-acids in the polypeptide chain contain in the side chains active functions capable of forming complexes with metal ions, or doing reducing, sulfide forming, and condensing reactions. On the other hand, gelatin inevitably contains reducing, sulfide forming or inhibiting impurities from the biogenic material and the manufacturing process [4- 6]. The increased sensitivity of the gelatin emulsions [7] opened the way for empirical testing by introducing into the emulsion various materials (some strange ones). Thus, the spectacular effect on the sensitivity of mustard extract, which contains organic sulfur derivatives [8], has been discovered. Later [3] it was found that by introducing dyes into the emulsion, the range of spectral sensitivity increases from natural sensitivity to UV and blue, to green and then to red and infrared, opening the way for chromatic sensitivity and more accurate color rendering in black and white tones. By the 1936s, Koslowski and Mueller [9] discovered gold sensitization by introducing the thiocyanate gold complex into the emulsion. * email: vladimir.bacarea@umftgm.ro, bacarea@gmail.com, Phone:+ 40744645744 All of these random experimental discoveries, alongside the spectacular applicative importance, made damage for a clear understanding of the mechanism of photosensitivity. Scientific thinking in the field has entered in the paradigm of introducing into the emulsion various compounds that react to the surface of the grains producing sensitivity or fog centers or chromatic sensitizer aggregates. Thus, Trivelli [10] showed that the art of preparing high sensitivity photographic emulsions can be viewed primarily as the art of introducing impurities into AgX in a particular way, and Sheppard [11] states that sensitization is achieved by forming on the surface of the grains of tiny deposits of silver sulfide produced from the normal sulfur compounds present in gelatin ”. It is paradoxical, but it has been shown that a single AgX granule sensitivity center, which can provide developability after exposure to light, is composed of several sulfur atoms associated with Ag and / or Au, but optimal sensitization requires about 10 5 sulfur atoms per grain [12]. A great deal of research work has been done to clarify the mechanism of sensitization [13, 14] and the nature of sensitivity and fog centers [15-19]. Over time, it has crystallized the idea that sensitizing agents introduced into the emulsion are adsorbed to the surface of AgX grains, where they react to form a silver sulfide film, mixed gold and silver sulfide, or a mixture of reduced silver or/and gold and sulfides [20] which then migrates on the surface concentrating into islets, but especially that these centers are formed on the surface defects of the grains [21-24]. J. W. Mitchell is the only one who suggests that sensitivity centers could be located in the gelatin layer adsorbed on the surface of the grains [25]. No one has raised the question that it is possible that the sensitivity and fog centers do not form directly on the surface of the grains, but in the intergranular aqueous medium and, once formed, adhere to the grains. This mechanism is not only possible, but also very likely, since the sulfur precursor micro-flux from the reaction mass to the surface of the grain intersects with that of the silver ions complexes coming from the grain to the reaction mass. The maximum concentration of the two reactants is at a certain distance from the surface of the grain. Then, if so, why not separate this processes of forming the sensitivity centers from that of the actual sensitization achieved by adsorbing them on the grains? Our previous, unpublished research has demonstrated that this mechanism is not only possible, but can also lead to particular application benefits in both fundamental and industrial research. We also appreciate that this approach, given the advances made in the past decades in the field