|Badarian flint knife|
A reader has asked, "Why did Zipporah use a flint knife to circumcise her son when she could have used metal? Didn't she live during the Bronze Age?"
It is true that Zipporah lived in the late Bronze Age (BC 1550-1150). She was the daughter of the priest of Midian. His name was Jethro and he was a descendant of Abraham, the Hebrew, by Abraham's cousin wife, Keturah (Gen. 25).
The Hebrew people were careful to preserve the ritual practices of their Horite Hebrew ancestors (their Horim). It was the tradition to use flint knives for circumcision. The ruler of Og (Numbers 21) slept in an iron bed. An iron bed was an innovation, but the Horim didn't encourage innovation when it came to sacred rituals such as animal sacrifice, the coronation of rulers, and circumcision.
It is likely that the knives were made of flint with a high sodium content. This would inhibit infection. The knife shown here was produced by a process called "knapping." Some of the oldest and largest collections of knapped stone tools has been found at Kathu in South Africa.
For further information, read Zipporah's Flint Knife; Circumcision Among Abraham's People; The Origins of Circumcision, Circumcision and Binary Distinctions