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Snowflake. Coloured low-temperature scanning electron micrograph (LT-SEM) of a snowflake. To prepare for the imaging process the snow and ice crystals are collected on copper sample plates containing pre-cooled methyl cellulose solution. The plates are then rapidly cooled to -196 degrees Celsius in a bath of liquid nitrogen. The samples are then either held in storage or photographed using a field emission scanning electron microscope that has been pre-cooled to -170 degrees Celsius. (KEYSTONE/SCIENCE PHOTO LIBRARY/ARS/US Dept of Agriculture/SCIENCE PHOTO LIBRARY)