Let's explore the fascinating history of film colour sensitivity and the discoveries that made the production of infrared film possible...
All early photographic materials - up to around the late 1880s - were sensitive to blue and ultraviolet radiation only. Looking at early photographic prints you will often find evidence of this in their empty white skies - the negatives having blocked out highlights from the blue sky. If clouds are prominent, they are probably the result of a different exposure - and sometimes one taken in quite a different place under different conditions, with many photographers making a small collection of cloud negatives using brief exposures that were then added to pictures in the darkroom.
One well known picture using this method is Camille Silvy's "River Scene" from 1858, which was the subject of a book by Mark Haworth-Booth of London's Victoria & Albert Museum.
Camille Silvy, 'River Scene', 1858
The technique was not invented by Silvy, but had been used even earlier by others, including Hippolyte Bayard, who had widely publicized the method.
The history of film colour sensitivity continues with the discovery of the german chemist Hermann W Vogel (1834-98) in 1873 that it was possible to make photographic emulsions sensitive to longer wavelengths by adding small amounts of certain aniline based dyes. His work that was extended by others including J M Eder, who introduced the use of the dye erythrosine in 1884 (also known as FD & C Red No 3).
This led at first to the production of "isochromatic" or "orthochromatic" plates, which were sensitive to green light as well as blue and ultraviolet, giving much better tonal rendition. Orthochromatic materials are great for films for darkroom use, as they can be handled in a bright deep red safelight, enabling orthochromatic films to be developed 'by inspection'. In older, less safety concious days, many photographers would actually judge their negatives by holding a lit cigarette behind them.
Other than for special purposes such as X-ray and scientific films, ortho films are fairly hard to find now, and generally slow materials for darkroom use. One company still producing camera speed ortho material is Maco. Their ORT25 is a high contrast film (roughly 50ASA), excellent for copy work and forensic photography, while PO100 is a lower contrast film that has applications in scientific fields such as astrophysics and medical photography and can be used for portrait and studio work with an orange filter. Because of their high resolution, these films produce extremely sharp, grainless negatives. Both ORT25 and PO-100 are available in 135, 120, and 4x5 sizes - even 8x10 on request.
The history of film colour sensitivity made a step further around 1902 with the introduction of isocyanine dyes by Arthur Traube and Adolf Miethe which made possible the creation of panchromatic emulsions - sensitive to the whole range of visible light . Later improvements by Dr. Benno Homolka in 1907 included the whole red region rather than just the yellow and orange of these early materials. The first panchromatic films were made in 1906, although they did not become widely available for amateur use until the 1930s.
Early panchromatic materials were also generally made with low sensitivity in the green region to allow limited inspection during manufacture, and also tended to lack sensitivity in the red region. It was these defects that led to the advice to use a yellow or yellow green filter to get more normal tonalities and also to the widespread use of orange and even red filters to get more impressive skies. With modern panchromatic materials, filters are generally only necessary to provide a distorted tonality either to meet expressive or technical requirements.
Some dyes (notably the dicarbocyanines) were found to give little or no sensitivity in the green and yellow area of the spectrum, but greatly increased sensitity in the range 650-820 nm - red and infrared. This made the production of infrared film possible.