seeing red

Ansco Panchromatic film advertisement in 1955

Toronto. Nope, this isn’t about anger issues – or bulls – but good old films and emulsions. All emulsions and sensors are sensitive to light. The energy of light varies with blue and shorter wave lengths having proportionally more energy.

The light energy falls as light goes from blue to yellow to green to orange to red and below. Early emulsions were blue light sensitive. Some times a chemical sensitizer was used to make the emulsion sensitive to some lower wavelengths. For example, Orthochromatic film was sensitive to blues through yellows in the visible spectrum.

This meant films could be safely developed in a red or orangish light – orthochromatic emulsion couldn’t see red or orange. Hence the use of safelights in darkrooms. Further, the film was initially about a third the cost of panchromatic emulsions which appeared around the time of the great war (WW1). Orthochromatic films had trouble with lips and skin tones. Lips were black, clothes were shaded differently based on colour, skin came out too dark, or mottled, etc. At the blue end of the spectrum, there was no differentiation between clouds and sky as both appeared very light in prints (unless a yellow filter was used to darken the sky without affecting the clouds as much).

Movies of the late 19th and early 20th century used special make-up, lighting, filters, etc. to compensate but they soon reverted to panchromatic media. Amateur stills stayed with the cheaper orthochromatic emulsions until the mid 1950s when both Ansco and Kodak switched to panchromatic films forcing film development to a totally dark environment whether a special daylight developing tank or just a totally dark room. In April of 1955, Ansco touted its pan films, followed a year later by Kodak and its Verichrome Pan.

Black and white printing always used orthochromatic materials since panchromatic films did all the heavy lifting to correctly balance the scene colours to shades of grey. Use of two emulsions and filters to change the paper’s H&D curve is another very interesting story.

George Dunbar found the LIFE magazine ad shown here in its April 18, 1955 issue on pages 56 and 57.

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