In this review the evolution of the concepts of AgHal spectral sensitization by the organic dyes is presented. The author comes to the unexpected conclusion that the very first chemical theories of spectral sensitization are, in essence, correct. One hundred years of detailed investigations of spectral sensitization have, in fact, proved the correctness of the early chemical concepts of spectral sensitization processes.
The reaction rates for the conversion of AgCl to AgClBr were studied qualitatively using a reflection spectrophotometric technique. The conversion rate was found to be dependent upon many factors, including the source of bromide and the presence and concentration of ripeners and restrainers. Soluble bromide (KBr) reacts faster with AgCl than does AgBr. Ripeners (1,1,3,3-tetramethyl-2-thiourea, 3,6-dithia-1,8-octanediol) greatly increase the rate of halide conversion. 4-Hydroxy-6-methyl-1,3,3a,7-tetraazaindene greatly reduces the rate of halide conversion or can completely eliminate it using either soluble bromide or AgBr as the bromide source.
The photographic emulsions, which consist of suspensions of silver iodobromide nanoparticles in fish gelatin, were made by a double-jet method. The average sizes of the particles obtained by XRD measurement and TEM observation were 16 nm and 14.3 nm, respectively. The microwave photoconductivity measurement showed two first-order kinetic processes. The electron lifetime in the first process shortened obviously, indicating a mass of shallow traps on the nanoparticle surfaces. The second process was a slower decay one, which was considered as electron trapping followed by the reaction of trapped electrons with interstitial silver ions. A higher maximum frequency obtained in the dielectric loss measurement indicated formation of interstitial silver ions with high concentration on the surfaces of the nanoparticles. For sulfur sensitized nanoparticle emulsion, sensitivity and gamma increased with increase of both amount of sulfur sensitizer and sensitizing time, but the excessive amount of sulfur sensitizer rapidly led to the occurrence of additive fog density. In the case of the optimum sensitivity and gamma, sulfur sensitization centers, i.e., dimers of Ag2S on the AgBr/I nanoparticle surface can be roughly estimated as no more than 500. The addition of methionine (Met) and methionine sulfoxide (Metsox) in the emulsion at chemical ripening made the density—(log exposure) curves shifted to lower exposure which demonstrated that their effective sensitization attributed to the bromine acceptance and to reducing the power of these additives.
Heavy hydrogen hypersensitization formed P centers, which were silver nuclei acting as electron traps on octahedral silver bromide grains in coated emulsion layers. The number of P centers was evaluated by measuring the diffuse reflectance spectrum of a stack of 10 coated emulsion layers. Sulfur sensitization centers increased the rate of formation of P centers, and decreased its activation energy. The observed activation energies were 0.87 eV in a primitive emulsion and 0.52 eV in an excessively sulfur sensitized one. This result supports an idea that sulfur sensitization centers formed on silver bromide emulsion grains catalyze silver nuclei formation, and that this is one of the essential functions of sulfur sensitization centers.
Effects of several inhibitors on contrast of physical developed silver in one-sheet DTR (diffusion transfer reverse) system were studied in this article. In this DTR system, the general measured reflection density could not be directly adopted because it was a comprehensive value of physically developed silver on the surface and chemically developed silver in the emulsion. For this reason, a one-dimensional CCD instrument was applied to monitor the reflected light intensity during development. The light intensity was accepted to describe the amount of physically developed silver of each exposed step on plate, then the contrast coefficient could be calculated out from the curve of light intensity versus logE. It was found that some inhibitors could improve the contrast of physically developed silver image accompanied with an improvement on sensitivity in this one-sheet DTR system.
By using a high-quality Ag(111) film covered with a bromide monolayer (a monolayer model of the AgX surface) as the substrate well-defined solubility equilibria were observed for the first time for the two-dimensional (2D) J-aggregate of pseudoisocyanine (PIC) perchlorate in both aqueous and ethanolic solutions. The 2D J-aggregation isotherms gave a sharp rise at a well-defined critical dye concentration or threshold reflecting the characteristic solubility of the PIC 2D J-aggregate, which was several orders of magnitude smaller than that known for the homogeneous J-aggregation in a far more concentrated aqueous PIC solution. The results allowed quantitative determination of the solubility product and the related thermodynamic functions. The measured enthalpy of dissolution, together with the approximate solvation energies of PIC cations and ClO4− anions in the polar solvents, suggested an absolute molar cohesive energy of the PIC 2D J-aggregate of around ∼500 kJ/mol. This large cohesive energy supports the capability of PIC cations and counter anions to form a stable 2D ionic crystal. Experimental hints are also provided as to how the solubility of such a 2D ionic crystal is affected by its physical size and by an excess concentration of common ions in solution.
We have proposed in one of our former reports a new definition of dot gain for halftone prints. The direct measurement of the ink layer thickness involved in the definition of mechanical dot gain is time and labor consuming, and thus colorimetric measurements are the best way of determining the degree of dot gain from a practical viewpoint. The present report tries to quantify the degree of colorimetric dot gain in terms of the conventional Yule—Nielsen n. By assuming the n value to be constant over the entire visual spectrum, the spectral reflectance of a halftone print is calculated in order to derive the corresponding chromaticity coordinate. The change of the n value with halftone frequency and marking systems indicates that the n value correlates well with the degree of mechanical dot gain estimated from the microscopically observed dot structure. By using n as the measure for dot gain, it is possible to compare the degree of dot gain between prints differing in color saturation.
This work compares the luminance level of photographs of the face on the Turin Shroud with other experiments. Luminance levels are analyzed in order to extract 3D information. Comparisons may aid in better understanding of how the image formed. Four significant photographs of faces are analyzed by a new technique to correlate the black-and-white luminance of various photographic images with the image on the Shroud. Three photographs of the facial image were used to verify the stability of the results, according to variations in the photographic characteristics of the same subject. After normalization of each digitized image, areas corresponding to various classes of gray were highlighted, in correlate them with 3D information on the distance between face and Shroud. All the photographs except that of the “Edessa Mandylion” show some 3D characteristics and the Shroud photographs, although disturbed by many defects, seem to correlate well with the sheet-face distance. Perhaps the best 3D results are those yielded by the carbon dust technique proposed by E. A. Craig, although it presents many open questions regarding formation mechanisms. With respect to the photographs of the Shroud, the experiments of V. Pesce Delfino and J. Nickell show a much higher percentage of saturated pixels correlated with areas of non-contact between face and Shroud. This fact is in contrast with the hypothesis that the body image of the Shroud formed according to the technique proposed by the above researchers.
The validity of fluorescence microscopy was investigated for imaging microcontact printed (μCP) patterns prepared by chemical modification on a glass surface. Lithographic stamps were used for patterned silanization of a glass surface, followed by chemical modification with a fluorophore. The stamped patterns modified with a fluorophore on the surface were analyzed using fluorescence microscopy. The observed fluorescence patterns were confirmed by spectral measurement to be from the fluorophores bound to the silanized pattern. This method of modifying patterned surfaces using fluorophores provides a simple way of high-lighting microprinting, taking advantage of chemical modification of μCP patterns.