Fig. 1

Water in different aggregation states observed with reflected-light microscopy: a Image of a droplet of water in polarised light; polarisers are orientated parallel to each other. b The same droplet of water disappeared when polarisers are crossed. c Ice crystals could hardly be seen with parallel orientated polarisers. d Under crossed polarisers, ice crystals became much clearer, while the background completely darkened. (Distance between object and objective was the same in a/b and c/d; no image processing was performed). White bars indicate 500 µm