Winter is coming to an end; the last nights of below zero temperatures are here. In the morning, one still spots the occasional icicle on a gutter or car bumper. When you look at these icicles carefully, you may notice that they show a characteristic pattern of ripples — always around one centimetre wide. What causes these ripples? Using an icicle machine of their own design, physicists and chemists investigated this question, and discovered that salt plays an important part in the formation process of the ripples.
