how many carrots in a gold ring?

“Why is that gold ring a different colour from that gold ring?” asked my daughter.
 
“Because they use different carat gold,” I replied.
 
“Carrot gold?” said my daughter.
 
“Yes, this one is 18 carat gold, so it looks, well, brassier than this one, which is nine carat gold.”
 
“Nine carrot gold?” asked my daughter.
 
Well, you can see the problem here, and it did suddenly make me wonder where the word carat came from.
 
Yes, it’s another etymology post!
 
Deep breath…
 
Carat (or karat for our North American chums) comes – via a long and winding road heading back through Middle French carat, Latin carato and Arabic qirat – from, in the very beginning, the Greek kerátion (κεράτιον), meaning carob seed (or, literally, “small horn”).
 
Whaaaat?
 
What do seeds have to do with the quality of gold?
 
Well, it was all to do with the weight of said carob seeds, which was deemed (wrongly, of course) to be steady and unchanging.
 
From the Greek kerátion, the Arabic term quirat came also to mean “weight of five grains”, a unit of mass.
 
And this unit of mass – the quirat – came to be used to describe the purity of gold, or how much pure gold was being used in an item.
 
Now, in jewellery, 24-carat gold is essentially pure; 18-carat gold is 18 parts gold, six parts another metal alloy; and so on.
 
Carat is also used as a metric unit to measure the weight of precious stones, and is equal to 200mg, so you’ll hear about a two-carat diamond, for example.
 
No carrots, though.