Centuries ago, the Jews of Central Asia were easy to identify; they were the ones with blue hands.

The Jews of Tajikistan were predominantly in the cotton and silk trade, specializing in the dyeing process. Making the dye — which came from the dried bodies of the female cochineal insect and indigo — caused their hands to stain.

That is just one of the many little-known facts about Jews around the world that appear in Ken Blady's new book, "Jewish Communities in Exotic Places."

Blady, who lives in Berkeley, has taught classes and lectured widely on the subject. He will be teaching a course this fall through the extension program at U.C. Berkeley.

A history buff, Blady could probably explain all of civilization in half an hour. In a recent conversation, he took a reporter on a journey from the destruction of the First and Second Temples to his childhood in a Chassidic enclave in Brooklyn — which he does not consider exotic. Along the way, he stopped in the Byzantine, Babylonian and Ottoman empires, to name just a few.

Jews in exotic lands have long held a fascination for him, ever since he can remember.

Perhaps it has something to do with the fact that his own mother and grandfather, who were Chassidic Ashkenazi Jews, took refuge in Uzbekistan during World War II.

And when he was 6 or 7, he shared a bunk bed with a black Chassidic Jew at summer camp. "I was too young to interview him and find out his story," Blady said.

For his book, Blady chose Jews of Eastern, non-Ashkenazi, origin who did not live in or come from major Jewish centers. Because of their isolation from other Jewish communities, they developed unique customs, often adopting traditions from the dominant culture in which they lived.

For instance, he said, although custom dictates that Jews are to welcome strangers to the seder table, cave-dwelling Jews in Libya invited no one for Passover. Many Libyan Jews had fled Spain and were hidden, Crypto-Jews, practicing their Judaism in secret.

Some Persian Jews believed that eating the foreskin of a newly circumcised baby could cure an infertile woman.

Yemenite Jews considered grasshoppers kosher.

And in Dagestan, Jews were "fiercely Jewish," the result of living in a climate in which clans continually fought one another. In one custom the Jews adopted, if someone was killed, the victim's clan had three days to retaliate. The killer, however, had several options. He could flee, and if he eluded capture for three days, he could return. But then he was obligated to marry the victim's sister, "to replenish the blood he had shed," said Blady.

Another alternative for the killer was to attack the oldest woman in the clan, after which he would put his lips on her breast. When he did so, they were considered mother and son, and the two clans could no longer go to war because now they were the same family.

Beyond describing such foreign — and certainly exotic — customs, Blady hopes his book will clear up a common Jewish misperception.

"Most Jews in the world tend to think there are Ashkenazim, and that anyone who has a permanent suntan is Sephardic. It's a terrible stereotype, and we need to understand who the Jewish people are."

Beyond Ashkenazim and Sephardim, there are many more distinctions among Jews, Blady said. While the Ashkenazim are those who came from Roman lands after the destruction of the Second Temple, settling in Western and Central Europe, Jews of Eastern origin can be divided into several ethnographic groupings.

Among them are the Romaniote Jews. Originally Greek-speaking, the Romaniotes were Jews driven into Roman lands after the destruction of the Second Temple and Bar Kochba revolt, and lived under Byzantine rule.

And the group known as Mizrachi, or Eastern, Jews can be further broken down into two groups, Blady said.

One group, called Mista'aravim, lived in large communities in Arab lands, in such cities as Baghdad, or Fez and Casablanca in Morocco. These Mizrachi Jews had access to rabbis and other Jews.

However, the more isolated Mizrachi Jews, who are the subject of Blady's book, "lived in xenophobic environments and were often not allowed to make contact with the outside world," he said.

Perhaps the most isolated, Blady writes, are the Ethiopian Jews. And he suggests that their traditions emulate those of Orthodox Christians more than those of other Jews.

Blady conducted most of his research in Israel. He interviewed scholars there because paying a visit to such areas as Afghanistan, under the extremist Taliban regime, would do nothing to shed light on past Jewish life there.

"I tried to reconstruct life as it was lived in the 18th and 19th centuries," said Blady. "I was not interested in the modern day. I wanted to know what life was like 100 years ago, when Jews' lives were not influenced by outside sources."