Excerpt from HMP 7 Chapter 5
Other Recording Materials
This chapter will discuss the following holographic recording materials:
• photopolymer films;
• dichromate gelatin;
• photoresist (solutions and pre-coated plates);
• and photo-thermoplastic films.
If you are reading this chapter you are probably a practicing holographer or someone interested in investigating recording materials other than silver-halide emulsions. In either case, you are likely to know that the primary supplier of silver-halide emulsions (Agfa) has recently ceased production. As the last chapter states, other suppliers of silver-halide emulsions have begun to increase their production and distribution in order to meet the existing demand for these materials.
However, many holographers and hologram production facilities are unaffected by this change of suppliers as they rarely use these silver-halide emulsions to record the type of holograms that they sell. Many users prefer the visual attributes or require the physical properties that holograms made on other recording materials offer. In fact, it is probably safe to say that most high-volume industrial and commercial hologram manufacturers do not use silver-halide emulsions at all, unless their replication systems copy silver-halide masters.
For instance, clients that need relatively deep-image, highly-detailed, easily viewable display holograms for security, advertising, signage, or giftware products are increasingly choosing photopolymer film to make their holograms on. Industrial users also find them ideal for HOE applications. They combine the imaging qualities of silver-halide glass plates and films with the high-speed, high-volume capability of embossed hologram production.
Over the past decade, photopolymer recording materials have become quite cost effective to use. Per square inch, the unexposed photopolymer cost much less than silver- based films. In addition, with the proper laser it is possible to do both mastering and replication on photopolymer, which can lower manufacturing expenses. Most importantly, since exposure, processing and finishing procedures can all be automated using high-speed equipment, replication costs are significantly reduced – which should further increase the appeal of these holograms to all end-users.
Another recording material, dichromate gelatin (DCG), is undergoing a slight renaissance, as holographers all over the world have begun to research photosensitive materials that they can make themselves using easily obtainable ingredients, thus alleviating all potential supply problems. Although the giftware market has slowed drastically since the days when a considerable number of retailers carried jewelry and watches made with DCG holograms, this material could become more widely used by artists and other display holographers equipped with the proper lasers. We encourage any holographers with the patience and know-how to experiment with DCG.
Due to the fact that embossed holography requires a surface relief hologram to replicate, photoresist is now probably the most widely used recording/mastering material. As many readers know, the use of embossed holograms has skyrocketed since the packaging and security industries have integrated the technology into their production lines. Although most hologram manufacturing plants use the same photoresist formulations that they always did, commercial users have pushed suppliers to provide larger pre-coated plates, while still retaining quality. Some facilities have even begun to coat their own plates in custom sizes. Instructions for doing this are included in this chapter.
It is important to mention photo-thermoplastic recording materials in this chapter, too. These films, along with the "instant-hologram" cameras that employ them, offer benefits that other recording materials and systems can’t. Industrial holographers doing Non-Destructive Testing might be most interested in following developments in this field. However, educators, researchers and even embossed hologram manufacturers could find photo-thermoplastic systems extremely valuable in their work as well.
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