An Israeli tourist walking the alleyways of the great market of Cairo, Khan al-Khalili, is bound to hear some familiar words about the price of this or that product or praise of its quality coming from the Egyptian merchants, particularly the jewelry merchants. These words are a secret language that the merchants adopted to outsmart customers, so discovered Israeli researcher Gabriel M‫.‬ Rosenbaum of the Hebrew University in Jerusalem.

After he first heard the Khan al-Khalili merchants speaking Hebrew, professor Rosenbaum decided to research this phenomenon in-depth and discovered a whole new world. It turns out that the origin of the code used by the jewelry merchants dates back to the Middle Ages, when most of them were Karaite Jews.

“When I got back to Israel, I went to Jewish-Egyptian friends and Karaite Israelis. There is evidence of the existence of a Hebrew code among the guild of metalsmiths as far back as a thousand years ago. I cross-checked it at the Khan al-Khalili market and in Alexandria, and I also visited the metalsmiths’ streets in two towns in the Nile Delta, Tanta and Damanhur. I read up on secret languages, and I learned terms from the field of metalsmith tools.”

Thus, for example, in market jargon the word yaffet means "good" or "nice," similar to its meaning in modern Hebrew. The merchants use it to share information about clients who look wealthy or give their opinion of a good product. “The opposite of yaffet is ashfoor,” says Rosenbaum, “a word whose root is unknown, and which does not suggest a Hebrew parallel.”