These are images of individual snowflakes as viewed under the power of a specialised low-temperature electron microscope and coloured by an artist. The images reveal the detailed physical structure of each snowflake. Capturing images of snow in the electron microscope posed a special challenge for US microscopists William P. Wergin and Eric F. Erbe. First they collected snow samples and then froze the snow, yes, froze an already frozen object, using liquid nitrogen. This brought the temperature of the sample down to minus 195 degrees Celsius. The flakes were then coated with a thin layer of platinum and place within a cold scanning electron microscope (SEM). There, the SEM passed a beam of electrons over the crystals' platinum surface, shaking loose their secondary electrons. These were then recorded by a special detector in the microscope and reproduced as black-and-white SEM snowflake images at up to 20,000 times magnification. "To our knowledge," says Wergin, "that was the first time snowflakes had been photographed using an SEM."