THEME: Knowledge Base 

28 JAN 2025

 

Have you even wondered where the term Carat comes from? And what is the difference to Karat?

Carat is the unit that measures the weight of diamonds and precious stones.

Karat is the unit that measures the purity of gold.

So, the two terms even though they sound the same, they are spelled differently and measure different things. Does this mean that the two units have different origin? No, it does not!

It all starts in Greece

The name Carat goes back to ancient Greece and the seeds of the carob tree (or χαρούπι in modern Greek).

The seeds of the carob tree are nested in hanging pods called keration, a term originated from the word keras which in ancient Greek means animal horn, this is because of the shape of the pods.

The seeds were historically used by merchants and traders who needed a reliable unit to measure the weight of precious gems and gold. Carob seeds were perfect for this task, as they were known for having a uniform weight which is approximately 0.20gr and they could be found in abundance in all regions across the Mediterranean basin.

What about Karat? And what does the number 24 signify?

To answer these questions, we need to go to the Easter Roman or Byzantine Empire. 
The Roman Emperor Constantine I, moved the capital of the empire from Rome to Constantinople (meaning literally the city of Constantine), in 330 AD. A few years before that, Constantine had minted a new coin called solidus which replaced aureus and it soon became the coin used across the Byzantine Empire. 
Each coin was made by almost pure gold that weighted 24 carats (yes, the carob seed!) or about 4.5gr of gold per coin. 

A few centuries later, to facilitate trade, a lighter version of the coin begun to be minted called siliqua which was equivalent to 1/24 of the solidus.

“Siliqua vicesima quarta pars solidi est, ab arbore, cuius semen est, vocabulum tenens.”
A siliqua is one-twentyfourth of a solidus and the name is taken from the seed of a tree.

—Isidore of Seville, Etymologiarum libri XX, Liber XVI, 25

Image: https://www.doaks.org/

And then what happened?

The coin spread through trade routes across the empire and was used by the Arabs who called it qīrāṭ. It was then passed back to the West and we come across it in medieval Europe as caratus (or carratus) in Latin and then carato in Italian.

Image: https://the-rearview-mirror.com/

Modern times

The use of the Carat as measuring unit for the weight of precious stones was eventually formalized in 1907, when the Fourth General Conference on Weights and Measures adopted the metric carat as a standardized unit, defining it as exactly 0.20gr. This standardization was crucial for the global gemstone industry, providing a consistent and precise measure for trading and valuing precious stones.

The use of Karat as a measuring unit for gold purity remained unchanged since the time of the Byzantine Empire and refers back to the weight of the pure gold solidus which was equivalent to 24 carob seeds!

 

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