Iridescent effects are used widely in colour cosmetics products, as well as cosmetics and personal care packaging, as manufacturers attempt to grab the attention of the consumer. Currently the manufacture of consumer products with iridescent effects is expensive and energy intensive, however scientists from the University of Oxford and the Natural History Museum in London claim to have found a way of creating a similar effect that is cheaper and greener. Iridescence describes when the colour of a surface appears to change depending on the observer's position. It is produced when light is reflected off multi layers of transparent surfaces. Some of the light rays will be reflected by the upper surface of the material and some from the bottom surface. If the two light waves are out of phase - their wavelengths differ by half or an odd multiple of half wavelengths - and many of these layers occur in parallel, an iridescent effect will be produced. At present the manufacture of products that have this effect involves the creation of thousands of miniature reflectors, however the effect can be seen extensively in nature such as in butterfly wings and the hard silica shell of the algae diatom, studied by the researchers. The scientists led by Professor Andrew Parker of the University of Oxford, UK, have investigated the possibilities of farming the diatom as a cheap, green way of producing iridescent effects. The process involves taking a diatom and immersing it into a cell culture medium that encourages cell growth. Furthermore, the culture medium can be altered in order to modify the properties of the iridescent properties of the shell. "It's a very efficient and cost-effective process, with a low carbon footprint" said Parker, adding that as the shells are biodegradable their eventual disposal and the environmental impact of the process are minimal. "Exploiting the tiny shell's remarkable properties could make a big impact across industry" added Parker, further explaining that the economic and environmental benefits could in future encourage industry to develop a much wider range of exciting products that change colour as the consumer views them. In addition, the researchers, who believe that that in two years the technology could be industry operational, claim that the process is extremely rapid. They suggest that in one month, one diatom can give rise to 100 million descendents. The research was conducted by scientists at the University of Oxford and the Natural History Museum in London, with funding from the Engineering and Physical Sciences Research Council.