A gold nugget has been made so light that it does not sink in a cappuccino. Though this technology might seem like a gimmick for the rich and famous, it actually has some fascinating technological applications, reports Phys.org.

The 20-carat gold nugget you see floating atop this cappuccino is actually a new form of foam. It's quite literally gold in foam form, the first time this state has been achieved for this precious metal. In fact, although it is nearly impossible to distinguish this gold foam from a conventional gold nugget with the naked eye, it is a thousand times lighter than regular gold. As can be seen in the picture, it is even lighter than milk foam.

"The so-called aerogel is a thousand times lighter than conventional gold alloys," said Raffaele Mezzenga, lead researcher on the project. "It is lighter than water and almost as light as air."

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The new priceless material is actually malleable by hand and consists of 98 parts air and only two parts of solid material. Floating it atop milk foam is not just for show, it's also symbolic. Scientists achieved this ultra-light form of gold by mixing solid gold with milk protein fibrils. The milk proteins were first heated, which produced nanometer-fine protein fibers, or so-called amyloid fibrils. Those fibrils were then placed in a solution of gold salt.

Interestingly, the process also allows scientists to tinker with the optical properties of the gold, even altering its color.

"The optical properties of gold depend strongly on the size and shape of the gold particles," explained Gustav Nyström, a postdoc in Mezzenga's group. "Therefore we can even change the color of the material. When we change the reaction conditions in order that the gold doesn't crystallize into microparticles but rather smaller nanoparticles, it results in a dark-red gold."

Other than for making the world's most expensive cup of coffee, the new material could have a range of practical applications. For instance, its lighter weight means it could be used to make ultra-light watches or jewelry, and its highly porous nature makes it ideal for chemical catalysis. Furthermore, it could lead to the development of specialized pressure sensors.

"At normal atmospheric pressure the individual gold particles in the material do not touch, and the gold aerogel does not conduct electricity," said Mezzenga. "But when the pressure is increased, the material gets compressed and the particles begin to touch, making the material conductive."