1891 Gabriel Lippmann – an inventor and physicist from Luxembourg – invented a process for recording colour photographs. The result is beautiful colour photographs with high resolution. Professor Hans I. Bjelkhagen shares with us how it works.
Few photographers today are familiar with the name Gabriel Lippmann (1845-1921), even fewer have seen a Lippmann colour photograph. Lippmann was awarded the 1908 Nobel Prize in Physics for his invention of Interference Photography, an early colour technique exploiting the phenomenon of optical standing waves. Lippmann’s prize represents the only time this prestigious award has been given for a photographic invention. However, the process proved difficult and impractical, exposures ran into minutes, the colours were difficult to view and almost impossible to copy. Only a minority of photographers recorded successful Lippmann photographs. Those who did were skilled in making and coating their own emulsions and dedicated many years to the cultivation of the technique. Despite the difficulties, Lippmann’s photography remains, to this day, the only direct process of true colour photography known. It is a technique of exquisite beauty, both technically and aesthetically. The ultra- fine grain plates, essential to the medium, display the highest photographic resolution ever achieved. The encoding of colour, as a periodic volume diffraction grating of pure silver offers excellent and unrivaled archival longevity.
History of Lippmann Photography
Gabriel Lippmann, professor of mathematical physics at the Sorbonne invented, demonstrated and mathematically formulated the process of interference colour photography, also known as interferential photography, or Lippmann photography, in the years 1891-1894. The process exploits the formation of standing light waves, by means of a mirror, and records these in a single-layer, panchromatic, ultra-fine grain, but black-and-white photographic emulsion.
The principle of Lippmann photography is illustrated in Fig. 1. An ordinary plate camera is used to form an image on the photographic plate. But the plate is loaded backwards with the emulsion side placed away from the lens and in optical contact with a mirror of mercury. The incident light waves interfere with their own reflections forming a standing wave pattern within the volume of the emulsion, with a periodic spacing of λ/(2n) that has to be resolved and recorded (λ is the wavelength of light in air and n is the refractive index of the emulsion). The colour information is stored locally in this way. The larger the separation between the fringes, the longer is the wavelength of the recorded light. When the developed photograph is viewed in white light, different parts of the recorded image produce different colours. This is due to the separation of the recorded fringes.
In this way Lippmann’s photographs reproduce all the monochromatic components registered on them. Since wavelength is relative to colour the spectra corresponding to the original scene can be reproduced with formidable accuracy, unlike any other colour photograph.
August and Louis Lumière (1893, 1897), Eduard Valenta (1912), Richard Neuhauss (1898), and Hans Lehmann (1908) contributed extensively to progress in this field. In Fig. 2, a Lippmann plate by Neuhauss is reproduced. The Lumière brothers made the first silver-gelatin emulsions for the process and produced the first ever colour portrait. The first Lippmann photographers had to make and coat their own emulsions. This was a very skilled craft, as the crystals in the emulsion had to be extremely fine-grain if any colours were to be recorded. Standard plate cameras of the time were suitable for recording Lippmann photographs. It was only the dark-slides which had to be adapted to flow mercury behind the emulsion. The processing of the colour photographs was done in a similar way by most of the photographers. They used a developer based on pyrogallol and ammonia, which was formulated to suit the particular emulsion. There was very little interest in making emulsions for Lippmann photography after this type of colour photography was succeeded by the Autochrome process introduced in 1907.
Modern Lippmann Photography
Recent progress in the development of colour holography has opened up the possibility to reinvestigate Lippmann’s photography. Modern examples of interference colour photography have been made using improved panchromatic ultra-fine grain recording materials combined with special processing techniques.
The Recording Material
Ultra-fine grain (extreme resolution) and panchromatic materials are essential for recording Lippmann photographs. These must exhibit extremely low light scattering, be practically transparent, and be able to resolve upwards of 10,000 lines/mm. It is very difficult to make ultra-fine grain emulsions and only a few people have been able to do that since the time Lippmann’s photography was practiced. However, the Russian colour holographic plates – Slavich PFG-03c, a panchromatic ultra-fine grain silver-halide emulsion (grain size about 10 nm), can also be used to record Lippmann photographs. The author recorded his first Lippmann photographs using Slavich PFG-03c in 1995. His recordings were made without mercury using only the gelatin/air interface as a reflector.
Recording Lippmann Photographs without Mercury
An old Eastman Kodak Co. (Folmer & Schwing Div.) Auto Graflex 4″x5″ camera equipped with a Kodak Aero Ektar f/2.5, 178 mm lens was employed. A modified Graphic Film Pack Adapter was used as a dark slide. The unexposed plates were loaded with emulsion side facing away from the lens, with black velvet behind to reduce scattering. The light reflected at the interface between the emulsion and air is the only light allowed to hit the emulsion, all other light in the dark slide has to be absorbed using flat black material.
Figure 3 shows the standing-wave pattern for the mercury reflector compared with the gelatin/air reflection. A node is located at the mercury reflector, an optically thicker medium than air, and coincides with the gelatin surface. The phase shift there is λ/2. On the contrary, an anti-node (wave crest) is located at the emulsion surface in the gelatin/air interface, an optically thinner medium than gelatin, which means, since no phase shift occurs in this case, a silver layer will be created at the emulsion surface after development. In the mercury case the first silver layer is located λ/4 inside the emulsion.
The principal of recording Lippmann photographs without mercury is shown in Fig 4. Figure 5 depicts photos of the Graflex camera and the modified dark-slide.
The processing of the Lippmann photographs is critical. Emulsion shrinkage and other emulsion distortions caused by the developer must be avoided. Among the old Lippmann developers, the Lumière pyrogallol-ammonia developer gives good results. To avoid shrinkage the plates are not fixed, only washed after development. This is not a problem since the developed colloidal silver is not light-sensitive.
Figure 6 demonstrates what a processed Lippmann photographic plate looks like when illuminated and observed in different ways.
- When the plate is viewed in reflected light, where illumination or observation is not performed perpendicularly to the plate, a negative image is seen.
- When the plate is studied in transmitted light, a red positive image can be seen caused by the absorption of light by minute colloidal silver particles in the emulsion.
- When illumination and observation is perpendicular in relation to the plate, the correct colour image is seen. The illumination has to come from a large diffuse area above the plate.
Figure 6 was recorded at Hengrave Hall near Bury St Edmunds on 17 June 2000. Exposure time: 4 min 45 sec at aperture f/11.
A modern Lippmann photograph is a portrait of the author reproduced in Fig. 7. The plate size is 4” x 5” and recorded on Slavich material in bright sunlight softened with diffuser. The exposure time was two minutes at aperture f/4. Skin tones are remarkably realistic in a Lippmann photograph.
When not using mercury it is much easier to record large Lippmann photographs, provided one has access to large photographic plates. Here is an example of an 8” x 10” plate recorded on 1 May 2000 in the Abbey Gardens, Bury St Edmunds. Recording data: aperture f/11, exposure time 3 minutes on a Slavich PFG-03c glass plate. The plate was developed in the holographic GP8 developer. The very high image resolution of the recorded Lippmann plate in Fig. 8 is demonstrated in Fig. 9, showing a detail of the recorded scene. The resolution is actually limited by the quality of the camera lens and not by the resolving power of the recording material.
Note: (Since conventional photography, analog or digital, cannot record the colours recorded in a Lippmann photograph, only by viewing real Lippmann photographs, one can appreciate the quality of them. It is also difficult to obtain the very high image resolution of the Lippmann images when reproducing them.)
- Bjelkhagen, H.I. (1999a) ‘A new optical security device based on one-hundred-year-old photographic technique’, Opt. Eng. 38, pp. 55- 61.
- Bjelkhagen, H.I. (1999b) ‘Lippmann photography: reviving an early colour process’, History of Photography 23, No.3, pp. 274-280. Lehmann, H. (1906) Beiträge zur Theorie und Praxis Direkten Farbenphotographie mittels Stehender Lichtwellen nach Lippmanns Methode. Freiburg i.Br.: Trömer.
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- Lumière, A. & L. (1893) ‘Sur les procédés pour la photographie des couleurs d’après la méthode de M. Lippmann’, Bull. Soc. franç. Phot. (2o série) 9, pp. 249-251.
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- Neuhauss, R. (1898) Die Farbenphotographie nach Lippmann’s Verfahren. Neue Untersuchungen und Ergebnisse. Encyklopädie der Photographie. Heft 33. Halle a.S.: W. Knapp Verlag.
- Valenta, E. (1912) Die Photographie in natürlichen Farben mit besonderer Berücksichtigung des Lippmannschen Verfahrens sowie jener Methoden, welche bei einmaliger Belichtung ein Bild in Farben liefern. Zweite vermehrte und erweiterte Auflage.
- Encyklopädie der Photographie. Heft 2. Halle a.S.: W. Knapp Verlag.