How was the tortoise shell used in ancient divination made?

First of all, the things to be divined are carved in the middle of the tortoise shell in ancient Oracle Bone Inscriptions (abbreviated as far as possible, within three words is appropriate), then burned on the fire, and the tortoise shell is taken out after it is cracked. If the crack doesn't pass through those words, it means a good sign. If the crack stops on the word, it means it is general. If the crack passes through those words, it means a bad omen.

Why do you use tortoise shells for divination?

As early as more than 2000 years ago, Luz asked Confucius this question seriously. This matter was mentioned in Wang Chong's Lun Heng in the Han Dynasty, saying that one day Luz asked Confucius: The bones of pigs and sheep can be divined, and the branches and leaves of reeds can also be divined, but why do people have to use tortoise shells for divination?

Confucius replied like this:

Divination is like a naive child who wants to ask why when he meets something. Maybe he will find a white-bearded grandfather first. He must be an experienced man in the eyes of children. Tortoise shell is the first choice for divination, because it has the longest life. It knows everything from ancient times to the present, so when in doubt, who can you ask without asking the tortoise?

Confucius' answer is very vivid, saying that divination with tortoise shell is like asking for advice from a wise old man, which is a very reasonable choice. Of course, we don't have to believe that Confucius really answered this question, but it must be a very convincing answer found by the ancients.