Musée de l’Holographie- Paris
The stability requirements inherent in the holographic process make it necessary to use a pulsed laser for any subjects other than inorganic, static objects. Living subjects, such as humans or animals, require a pulsed laser, which is almost invariably a ruby system. The wavelength of the ruby emission is
694.3 nm approaching the infrared.
The effect of this is to penetrate the subcutaneous layer of the skin, resulting in a wax doll or death mask like appearance.
Drawing on the early experience of the film industry, a make-up technique has been developed to overcome similar problems; this has been adapted and applied to portrait holography.
Holography involving physically unstable subjects such as animal, humans, plants and so on, necessarily requires the use of a – Q – switched pulsed laser in order to overcome the inherent problem of movement during the actual exposure period, whilst the finely resolved fringe pattern, generated by interference of of light, is recorded in the body of the photographic emulsion. It is almost invariably impossible to record living tissue detail in a frontally illuminated situation with a cw laser system.
There are only two practical pulsed laser commercially available which emit in the visible spectrum –frequency doubled neodymium yag (green) and the ruby (deep red). Typically, the maximum practical output obtainable from a Nd yag frequency doubled system is about 250 millijoules, with a rather inferior mode structure (although in fact, this is a preferred region of spectrum.
Ruby lasers, especially designed for holographic use, are commercially available up to 25 joules, - Q- switched, with excellent mode structure ; but the emission line is in the deep red (λ 694.3 nm), which, when –Q- switched using a Pockel’s cell, normally produce a giant pulse of a duration of around 25 nanoseconds.
Holograms of excellent quality highly suitable for transfer to H2 white light reflection or transmission copies, even of extremely mobile subjects are possible with the system. However, the nearly infrared emission presents cosmetic problems when used to record human flesh, as is the portrait work.
Medical applications of holography to show skin deformations involve using infrared illumination to penetrate the subcutaneous layer of the skin, thus affording some record of the underlying layers.
This penetration effect gives the skin a wax-like appearance.
The use of the laser ruby in holographic recording of bare skin has a similar effect on the image to that created by infrared light in photographic work, and results in that –wax doll- kike or –dead mask- effect common in many holograms of people.
This effect becomes particularly objectionable of the H2 transfer is made to produce a real image, although it is so noticeable if a virtual presentation is employed in the H2.
Furthermore, correct tonal rendition into a monochromatic image is impossible if a light of single color and narrow band width such as that emited by a laser, is used.
The situation is, in many respects, analogous to those of early kinematographic movies and photograph, where the response of photographic emulsion was not panchromatic and make-up technique were developed to obtain good tonal representation of the subjects.
In our work, over a number of years, we have used make-up not only for portrait work, but also for recording other areas of the body, up to whole nude figures onto one meter square holographic materials. Caucasians, Negroes and Asians have all been recorded.
Margot in front her portrait, painted by The same portrait was used by Margaret Benyon at the Museum of Holography Dominique Mulhem in an holopainting
Although the technique of application remains constant, regardless of racial differences, the actual make-up material used must be selected in order to give the optimum results.
The model Marie-France is preparing to become Marylin
Catalogue of the exhibition Paris in 3D at the Musée Carnavalet Paris 2000 pp 192-193 Paris musées Booth-Clibborn Editions
Make-up materials and application
A simple application of an opaque ladies cosmetic face powder, selected for its tonal rendition and fine texture, and applied over the entire skin surface to be visible in the hologram, is sufficient to avoid the waxen appearance of the skin.
Considerable care and skill are necessary, or the layer becomes visible, particularly if the H2 transfer produces an image plane or real image; similarly, stage make-up, which are of course generally textured and made to be viewed from a considerable distance, are totally unsuitable.
In some of our work, where we have recorded full nude figures, the entire body as been covered in this way. However, whilst avoiding the waxen effect, this does not obviate the tonal distortions which occur when a highly monochromatic source, such as the laser, is used.
We have developed a system whereby the subject is viewed through a deep red filter whilst make-up is being applied.
Dr John Webster control through a filter makeup of Anne-Marie Christakis
Particular attention must be paid to the lips and cheeks, the rose or red areas of the face. Red translated into monochrome is normally a darker tone; viewed in the deep red light of the ruby laser, it becomes white. White lips are objectionable.
Similarly, the cheeks require tone.
In place of red lipstick or rouge, we have adopted green eye make-up and use this, applying it to the lips and cheeks areas whist viewing them trough a monochromatic red filter.
In effect, the facial tones are painted in. Our experience has covered Caucasians, Asian and Negroes people. The basic technique remains the same, but the cosmetic powder applied to the skin surface is different.
It is true that certain holographers, in particular Ana Maria Nicholson, have produced delightful and delicate portraits without the use of special make-up. However, perhaps the secret of her success lies in the sensitive use of the virtual image in her reflection work.
In our experience, specially adapted make-up is invariably essential to good holographic portrait work with the ruby laser. Considerable skill is necessary for its successful application.
1. Proceedings of Third International Symposium on Display Holography Lake-Forest 1988 pp 399-401 2. Practical holography Graham Saxby Prentice Hall Special problems with holographic portraiture 1988 pp 265-266 3. Proceedings of SPIE Volume 1238 Three-Dimensional Holography : Science, Culture, Education pp 348-350 Kiev 5-8 September 1989 4.Fitfh International Symposium on Display Holography Volume 3358 Lake Forest College 1994
commenter cet article