In progress: Seeking additional comments and images to develop this section
Photographic Materials Conservation Catalog
Date: Initiated January 2012
Contributor: Laura Wahl
The Photographic Materials Conservation Catalog is created and maintained by the Photographic Materials Group of the American Institute for Conservation for the convenience of the membership. The treatments, methods, or techniques described herein are provided for informational purposes. The reader assumes responsibility for any application results or interpretation of information.
Identification/Visual Characteristics: Subjects in holograms appear to be three dimensional. Most holograms require relatively high light levels for viewing.
Support: May be glass, or plastic film (including PVC).
Historical: Derived from the Greek "holos", meaning whole message. Dr. Dennis Gabor was the first to imagine the theoretical possibility of the hologram in 1948. Early Gabor holograms were made with a single laser beam and are known as in-line phase holograms. True 3-D holograms could not be produced until more advanced lasers were made in the early 1960's.
Image Forming Materials
- Silver Halide: Particles on the order of 10 –100nm allow for higher resolving power than standard photographic films. Standard film has silver particles sized 0.2-2.0 microns/200-2,000 nanometers (Vitale) Such small particles in holograms equate to ISO/ASA of .025-1.6. This low sensitivity to light means that specialized supports and stabilizers, like sand boxes, are used to allow for the recording of holograms.
- Dichromated Gelatin: Due to lower sensitivity to light, it is most frequently used to mass produce holograms from a master, rather than for the original recording.
- Photopolymer: Due to lower sensitivity to light, it is most frequently used to mass produce holograms from a master, rather than for the original recording.
- Coating Materials: Reflection holograms on glass must be painted or coated on the verso to prevent transmission of light. Krylon paint (spray paint) has been used. Pressure sensitive adhesive (probably acrylic?) UV protecting films may also be applied to the recto (products such as MacTac brand)
- Color Holograms: Color in holograms is formed through a combination of development techniques, differing silver salts, using different colors of lasers, and/or by sandwiching three layers of holographic materials recorded with red, green, and blue wavelengths of light (recording of standing waves, similar to Lippman process in photography)