Nano Girl Michelle Dickinson: Truth about Olympics medals

Simone Biles of the United States poses with her "gold" medal after the artistic gymnastics women's individual final. Photo / AP

Athletes from all of the world have been going for gold in Rio, and some have made it - but what have they actually got their hands on?

As the Olympics come to a close this weekend, you may be surprised to know that this year's gold medals actually contain very little gold.

While we've watched our athletes collect their now-traditional medals, they are actually a relatively new concept to the Olympics.

Originally, champions in the ancient Games received an olive branch wreath at the closing ceremony and the 1900 Paris Olympics gave most of its winning athletes cups or trophies. It wasn't until the 1904 Olympics that the gold, silver and bronze medal tradition began, with each host country's organising committee being responsible for the design and production of the medal. Because of this, Olympic medals are unique to each of the games and this year Rio put sustainability as its focus for the medal design.

Making an Olympic medal involves first making a mould with the desired design images and shapes. The Rio team decided to spend two weeks creating their mould by hand with precision tools rather than using more modern high-tech equipment. They then scanned the mold into a computer controlled CNC cutting machine to create an identical full-size steel mould, which was heat-treated to make it tougher. The disc-shaped medal material was placed into the steel mould and squeezed with hundreds of tonnes of force using a hydraulic press which created the images from the mould on to the medal surface.

The pressed medals were then finished off by hand before a ribbon was soldered on, which this year was made from partially recycled polyethylene terephthalate fabric sourced from used plastic drinks bottles.

Gold medals were actually only solid gold for eight years, with the 1904 Olympics in St Louis introducing the gold medal as the prize for first place and the 1912 Summer Olympics in Stockholm being the last time pure gold medals were used.

At $30,000 of raw material cost for one 500g pure gold medal to be made, creating 812 solid gold medals for this year's games would likely have bankrupted the event before it started. Instead, this year the gold medals were composed of 494g of silver with 6g of gold coating.

The coated gold was specifically sourced to ensure that sustainable mining methods had been used. Chemically, mercury amalgamates to gold meaning they attract each other.

At $30,000 of raw material cost for one 500g pure gold medal to be made, creating 812 solid gold medals for this year's Games would likely have bankrupted the event before it started.

In some gold-mining techniques, mercury is mixed with gold-containing materials to form a mercury-gold amalgam which vaporises the mercury when heated leaving the gold behind. Even though some of us remember the glass thermometer days where we played with liquid mercury, it is actually highly toxic, causing damage to the nervous system at even relatively low levels of exposure. Because mercury vapour from mining can contaminate the atmosphere and water over long distances, causing harm to the environment and the miners, Rio's stance on using mercury-free gold was a good one.

The silver medals also shine with sustainability as 30 per cent recycled raw silver was used to make them. Items including leftover mirrors, waste solder and x-ray plates were used as a silver source, turning them into medals worth much more than their simple material cost.

And the bronze medals were also eco-friendly this year, being made from a mixture of copper, zinc and tin, with 40 per cent of the copper coming from the waste of the Mint of Brazil, where the medals were made.

So as we tally up our final medal count and welcome our athletes' home from Rio remember: all that glisters is not gold, but our Kiwi sporting spirit is priceless.