For instance, 15% silver supported on α-Al2O3 or silicates is a catalyst for the oxidation of ethylene to ethylene oxide at 230–270 °C. Dehydrogenation of methanol to formaldehyde is conducted at 600–720 °C over silver gauze or crystals as the catalyst, as is dehydrogenation of isopropanol to acetone. In the gas phase, glycol yields glyoxal and ethanol yields acetaldehyde, while organic amines are dehydrated to nitriles. Photography The photosensitivity of the silver halides allowed for their use in traditional photography, although digital photography, which does not use silver, is now dominant. The photosensitive emulsion used in black-and-white photography is a suspension of silver halide crystals in gelatin, possibly mixed in with some noble metal compounds for improved photosensitivity, developing, and . Colour photography requires the addition of special dye components and sensitisers, so that the initial black-and-white silver image couples with a different dye component. The original silver images are bleached off and the silver is then recovered and recycled. Silver nitrate is the starting material in all cases. The use of silver nitrate and silver halides in photography has rapidly declined with the advent of digital technology. From the peak global demand for photographic silver in 1999 (267,000,000 troy ounces or 8,304.6 tonnes) the market contracted almost 70% by 2013. Nanoparticles Nanosilver particles, between 10 and 100 nanometres in size, are used in many applications. They are used in conductive inks for printed electronics, and have a much lower melting point than larger silver particles of micrometre size. They are also used medicinally in antibacterials and antifungals in much the same way as larger silver particles. In addition, according to the European Union Observatory for Nanomaterials (EUON), silver nanoparticles are used both in pigments, as well as cosmetics. Miscellanea Pure silver metal is used as a food colouring. It has the E174 designation and is approved in the European Union. Traditional Indian and Pakistani dishes sometimes include decorative silver foil known as vark, and in various other cultures, silver dragée are used to decorate cakes, cookies, and other dessert items. Photochromic lenses include silver halides, so that ultraviolet light in natural daylight liberates metallic silver, darkening the lenses. The silver halides are reformed in lower light intensities. Colourless silver chloride films are used in radiation detectors. Zeolite sieves incorporating Ag+ ions are used to desalinate seawater during rescues, using silver ions to precipitate chloride as silver chloride. Silver is