Chemists figured out a color photo of the mid-nineteenth century

Colors in your photo the mid-nineteenth century explained the distribution of silver nanoparticles and silver chloride. Chemists have reproduced the method of Alexander Becquerel and denied other causes of color photographs: the presence of colored compounds or interfering periodic superstructure of silver nanoparticles. Article published in the journal Angewandte Chemie.

The first method of producing color photography was proposed by Alexander Becquerel in 1848, silver was deposited on the brass plate, then the plate was immersed in a solution of copper chloride for sensitization layer. The resulting plate was washed, dried and heated, after which it was ready to capture the moment when exposed to light. However, since that time there has been a serious debate about the nature of the coloration of the resulting photos. Some scholars, such as William Abney and Matthew Carey Lea, adhered to the hypothesis that in the process of aging in the record appear new coloured compounds of silver or copper, which are responsible for colouring of pictures. In a discussion with them joined Otto Wiener and Wilhelm Zenker — the supporters of the hypothesis of a periodic structure of parallel plates of silver in the amount of particles that become a cause of interfering standing waves, which are responsible for color perception. The Becquerel supported the hypothesis of pigment and with a Carey Lea suggested that the “folklorica” silver includes silver chloride AgCl and subchloride of silver, Ag2Cl, and that the color depends on the ratio of these substances. A third explanation offered Luppo-Kramer: exposure of the plate to light leads to the formation of silver nanoparticles of different sizes for each color meets your particle size.

Modern studies have shown that the plates, there is a new process, irradiation of the plate with visible light, called spectral photoadaptation — change not only the particles but the distance between them, which reduces the absorptivity of the plate. The same process explained by the specific dissolution of silver nanoparticles with a certain size. However, at the moment no one has conducted extensive research confirming any hypothesis.

Victor de Seul (Victor de Seauve)
with his colleagues got the picture by way of Becquerel and have held a full analysis sufficient to explain the causes of color in this system. According to them, the color arises from the surface plasmon resonance on silver nanoparticles, which is the absorption of light at a certain wavelength. On the phase of the light absorption occurs by two processes: photolysis of silver chloride nanoparticles of metallic silver and redistribution of silver nanoparticles under exposure to light depending on size and position relative to the particles of silver chloride.

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