A pioneer in this field was Ducos du Haurun a brilliant Frenchman. He took color photographs. Three different colored filters were used to capture negative shots developed on gelatin film. The yellow, red and blue layers were then assembled to produce a single print. Over time, Ducos du Hauron introduced practises to speed up the process.
French investigators have analyzed some of the 18th century pictures. They used x-ray florescent spectroscopy, synchrotron-based infrared (IR) spectroscopy and Raman spectroscopy to determine the chemicals used as pigments for the different colors.
Photographs taken in 1878 showed that Prussian blue was the ingredient used for the blue gelatin layer. Carmine lake was the foundation pigment for the red layer. A binding agent of glycerol or castor oil softened collodion in the procedure.
Much experimentation took place in those days. Analysis of images from other periods is ongoing. Modern techniques allow examination without damaging the subject material. It is indeed a growing field of scientific endeavor.
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