Colour Photographic Process

In colour photography the film is multilayer, each layer containing the chemicals required to produce one of the three additive or subtractive primaries. In practice, it is those processes which use the subtractive YMC primaries that dominate the market. However, even in these cases the additive process is used to record the blue, green and red components of light in three layers the yellow, magenta, cyan subtractive primaries being produced in subsequent processing.  

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Without a doubt the best known of the instant colour photographic processes is that invented and developed by the Polaroid Corporation. " The original Polacolor system led to the famous Polaroid SX-70 system in 1972. This is a dye diffusion system involving a dye developer in a tripack negative arrangement, placed on top of a receiver sheet, as shown in Figure 2.30. 

In the black and white photographic process, the dark areas result from the presence of reduced metallic silver, Ag. In the colour process metallic Ag is used to synthesize a dye of the appropriate colour, and all the silver is removed from the film. The photochemical reaction is therefore the same as in the black and white process, namely photoinduced electron transfer within the AgBr grains. 

Colour photographs must be taken at all sampling sites (stream water and sediment, residual soil, humus, floodplain sediment and optional overbank sediment), and recorded on the field observation sheets. Each photograph, after processing, should be carefully labelled at the back with a fine permanent ink and sent to the co-ordinator (Geological Survey of Finland) upon completion of the sampling. 

Mees, C.E.K. and James, T.H., The Theory of the Photographic Process, Macmillan, New York, 1969. Coe, B., Colour Photography The First HundredYears, 1840-1940, Ash Grant, London, 1978. Newhall, B., The History of Photography from 1839 to the Present Day, Museum of Modem Art, New York, 1988. 

The reproduction of colour in printing and photographic processes is by subtractive colour synthesis in which inks... 

Phil. Trans., 1842, cxxxii, 181-214 On the Action of the Rays of the Solar Spectrum on Vegetable Colours and some new Photographic Processes. J. F. W. Herschel used the name photography in Phil. Trans., 1839 he discovered that silver chloride is easily dissolved by a solution of sodium thiosulphate ( hyposulphite ) Edin. Phil. J., 1819, i, 8, 396 (26 f., 398 f.), and suggested its use in fixing to Fox Talbot, who used it early in 1839 Fox Talbot, Compt. Rend., 1839, viii, 341 (letter to Biot) Herschel, On the Chemical Action of the Rays of the Solar Spectrum on Preparations of Silver. . . and on some Photographic Processes Phil. Trans., 1840, cxxx, 1-59. 

Hershel JFW (1842) On the action of the rays of the solar spectrum on vegetable colours and on some new photographic processes. Phil Trans 132 181-214... 

Prussian blue is a mixed Fe(II)/Fe(III) complex polymeric species in which Fe(II) is octahedrally coordinated by C, and Fe(lll) is octahedrally coordinated by N, to give a structure containing Fe(II)-C-N-Fe(lll)-N-C-Fe(II)-linkages, in which the colour originates from electron transfer between the two metal oxidation states. It was discovered in 1704, and used in blueprints and also in the cyanotype photographic process developed by Herschel (see Chap. 11). The cyanotype process is made possible by the photochemical reduction of Fe(III) citrate (or oxalate) to Fe(II), which reacts with ferricyanide present in the coating formulation to give Prussian blue. A similar photoreduction of Fe(lII) oxalate to Fe(ll) is used in the ferrioxalate actinometer (see Chap. 14). 

Dithiobenzoic acid metal complexes, 2, 646 colours, 2, 646 Dithiobiuret metal complexes, 2, 640 Dithiocarbamates chelating resins mineral processing, 6,826 Dithiocarbamic acid metal complexes, 2,585 amine exchange, 1,428 photographic emulsions, 6,98 nickel poisoning, 6,768 tellurium(Il) complexes photothermography, 6,121 Dithiocarbazic acid metal complexes, 2,803 Dithiocarbimic acid metal complexes, 2,588 Dithiocarbimic acid, cyano-metal complexes, 2,808 Dithiocarboxylic acids metal complexes, 2,646 Dithiodiacetic acid metal complexes, 2, 806 Dithiodiketones... 

A variety of processes exist in which photographic images are produced as a result of a photoinitiated chain reaction. Such reactions, which are characterized by three fundamental steps (initiation, propagation and termination), provide the basis for certain processes in which photopolymerization, photocrosslinking or colour formation or destruction represents the main image forming stage. 

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