Scientists have created a new form of gold that's (almost) as light as air

The world's first nugget of gold aerogel.

The lightest form of gold has been produced by researchers in Switzerland, consisting of 98 percent air, 20-carat gold, and milk protein. While it retains the metallic sheen of its regular form, this new gold aerogel is made almost entirely of air, and it has a range of curious properties that give it potential far beyond the jewellery cabinet.

"The so-called aerogel is a thousand times lighter than conventional gold alloys. "It is lighter than water and almost as light as air." 

Mezzenga and his team produced the gold aerogel by making a three-dimentional mesh of gold that’s almost entirely made up of pores. Of the 2 percent of the material that isn’t air, more than four-fifths of it is 20-carat gold, and the rest is nanometre-fine strings of milk protein. (I guess that’s what inspired the researchers to top off a latte with the stuff in the image above).

First they had to heat the milk proteins up to produce the tiny fibres - known technically as amyloid fibrils - and these then were mixed into a solution of gold salt. Within this solution, the fibres became interlocked to form a basic structure, and the gold particles crystallised into even smaller particles around it. This formed a gel-like gold fibre network. 

The big challenge came next, when the team wanted to dry out the solution without destroying the fine network created by the milk protein fibres and gold. Rather than simply air-drying it, which would have been too harsh, they had to put it through a long and delicate process called supercritical drying, which is also used to decaffeinate coffee.

Throughout the process, the researchers figured out that they could tweak the colour of the aerogel by adding smaller particles of gold to the solution. "When we change the reaction conditions in order that the gold doesn't crystallise into microparticles, but rather smaller nanoparticles, it results in a dark-red gold,"