Silver Halide Materials

Silver Halide is the most common holographic material currently used by everyone from hobbyists to professional scientists. This is because of its high sensitivity and the fact that it’s easily available commercially. Silver Halide is a salt of Silver and a Halide, which are a group of elements that include Fluorine, Chlorine, Bromine and Iodine, which are light sensitive. The first, accidental, discovery of the light sensitive properties of Silver salts came in 1727 when J Schulze mixed chalk, Nitric acid and Silver in a flask. He noticed that the side of the flask turned toward the sun turned dark. The first deliberate application of this effect, a photograph of a scene, was carried out by Niepce in 1827. This was a long exposure of about 8 hours. In 1841 Henry Fox Talbot patented a “calotype” process which made a permanent negative image on paper soaked in Silver Chloride. The present day emulsion was created by Richard Leach Maddox, who proposed using gelatin and Silver Bromide in what he called the “dry plate process”. Shortly after that Eastman Kodak coated a flexible film with this as a thin emulsion, mass produced it, and launched large scale photography. Silver Bromide is only sensitive in the UV and blue regions and so dyes need to be added to it in order to make it sensitive to other colors. In holography, specific dyes are added to give the emulsion a high sensitivity at particular, commonly available laser lines.