If you dissolve sugar in hot water and then cool it down, you’ll see pure sugar crystals form while impurities stay in the liquid. You can even watch the beautiful sugar crystals slowly grow in the water.

You can do the same thing with metals, though probably not in your kitchen.

At high temperatures, one molten metal can dissolve another. As the mixture cools, the dissolved metal begins to crystallise inside the melt, just like sugar forming crystals from water.

In new research published in Nature Communications, we have observed this process in more detail than ever before – and used the information we gained to produce crystals that are perfect for harvesting hydrogen from water, in the first of countless possible applications.

There are important differences between water and liquid metals.

For one thing, we cannot see inside a........

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