Scientists from Estonia\'s University of Tartu have created a glass surface that can be rendered opaque in an electric field, allowing it to be used as window shades, local media reported Monday. The secret of the creation lies in a special spray-on gel, which after encountering the glass surface forms a 5 to 10 micrometer coat, the country\'s ETV reported. Upon encountering an electric field, the gel changes its optical properties at a flick of switch. So far, the gel has been applied to small square pieces of glass, which have passed all laboratory tests. Estonian scientists are now, however, trying to figure out how to apply the same technology on larger surface. According to Ilmar Kink, head of the Nanotechnology Development Center at the university, one option is to develop a special spray booth, which would apply the gel in an even coat. The glass can be used in office buildings and shopping malls. \"From a technological standpoint, we see no reason that it couldn\'t be used even on skyscrapers,\" said Kink, adding that if everything goes smoothly as scheduled, the processed glass will be in mass production within a year.