An extract from Scientriffic, CSIRO’s science magazine for ages 7+. In this article, you'll find out how opals are valued by their colours.
Opals are precious gemstones found mainly in outback Australia. Australia mines more opals than any other country. So, what colour are these opals? That’s hard to tell.
One stone might look blue and green from one angle and then look red and orange when you turn it a different way. CSIRO imaging researcher Leanne Bischof says, “Opals are like a hologram that changes patterns in the light. When you turn an opal in your hand, it flashes many different colours and patterns. That’s why they’re so beautiful.”
It can be very difficult for the human eye to see what colours are in an opal and exactly how bright they are. Jewellers want to know this information so they can decide which opals are the most valuable. Is it worth $200 or $20,000? Opals with lots of red, for example, are worth a lot more.
CSIRO and a group of opal miners have developed a machine to analyse the colour of an opal. The machine looks like a small cupboard. You put the opal inside the machine on a platform called a stage and shine a light on it. Then, a tiny camera takes hundreds of photos of the opal from lots of angles as the stage is rotated automatically. Smart mathematics and powerful computers then analyse all the images and work out how many colours there are, how bright they are and how much of each one there is.
Every opal gets a special code which jewellers use to decide how valuable it is. This determines how much pocket money YOU need to save up to buy it!
Sarah Wood
Read more about Scientriffic: a science magazine for ages 7+.
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