It was this dye that caused the additional colour sensitivity. Along with a number of preservatives the coating contained a dye, corallin, to prevent light penetrating through the film to the glass plate. He then isolated the coating applied to the plates as an anti-halation measure as being the cause. Vogel's Discovery of Optical Sensitizers Vogel was working with collodion dry plates produced by Colonel Stuart Wortley, he noticed that the sensitivity extended further than normal into the green range of the spectrum, thinking this was due to the developer used he carried out tests that proved negative.
Self-screen Ortho This referred to plates that contained an additional dye to balance colour rendering, other orthochromatic plates required the use of a yellow filter on the lens. Eder published details of an improved sensitizer, erythrosin, in 1884, soon after this orthochromatic plates were sold by most of the major manufacturers. Prior to this the sensitizing chemicals had to be applied by the photographer. In Britain these plates were produced under licence by B.J. The first ready-sensitized gelatine silver bromide plates to be sold were by Attout, trading as Tailfer and Clayton, in 1882/83. The idea of using sensitizers (dyes) to increase the range of colour sensitivity was first announced by Dr. These plates, also called Isochromatic, were sensitive into the green, and in part yellow, spectrum range. The first gelatine dry plates suffered from this problem, after the introduction orthochromatic plates, the older emulsions continued to be produced, generally known as 'ordinary'. As a result a false, or at least different, colour rendering was produced in a photograph blue objects appeared much lighter and yellow objects much darker. In contrast the human eye is most sensitive to yellow/green light. All of the early processes were principally sensitive to the blue/violet end of the spectrum.
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