> The conventional mixture is usually three- quarters gold and one- quarter copper, with a density of about 15 g/cm3.
That’s not true for this new lightweight gold: its density is just 1.7 g/cm3. And nonetheless it is still 18- carat gold.
Imagine comparing jewelry that is all “18 carat”, but some of it has 10x less actual gold. Seems like there will be a lot of fraud happening during a period when customers are not yet aware that the minimum amount of gold in an 18 carat piece has been reduced 10x. People will just hear “18 carat” and assume it means the same thing it meant before.