信口雌黄 (Xìn kǒu cí huáng)
Carry orpiment, an erasing agent, in one’s mouth—Let one’s tongue wag too freely
雌黄Cí huáng means “orpiment”, a yellow mineral used in ancient times as an erasing fluid. People in ancient China wrote on yellow paper. When they made a mistake, they used “雌黄 Cí huáng” to cover the wrong words and then rewrote on it. So 雌黄Cí huáng also means “making corrections on paper”.
Idle talk was the fashion in the Jin Dynasty. A court minister called Wang Yan (256-311) considered himself learned and often held forth in public. He finally became a well-known talker with quite a few followers. He liked to elaborate on Lao Zi (Laotzu) and Zhuang Zi (Chuangtzu), who advocated the theory of governing by doing nothing.
According to Lao Zi, enlightened administration is possible only when the ruler sets a good example for his subjects to follow instead of proclaiming restrictive laws and regulations which tend to interfere with people’s lives.
With a horsetail whisk in his hand, Wang Yan talked glibly in a manner as though he knew a lot about his subject. But he was often inconsistent in what he advocated. His listeners often pointed out his mistakes or threw doubt on what he said.
But he was undaunted and continued his ramblings. He was so thick-skinned that he would change his views without a second thought.
People mocked him with the phrase 口中雌黄(kǒu zhōng cí huáng) which means “orpiment in mouth”, suggesting he carried this correction fluid in his mouth.
Later this phrase became 信口雌黄(Xìn kǒu cí huáng) and came to stay as an idiom. People use it to describe those who talk without wisdom. When someone makes unfounded charges or deceitful statements, we also say: So and so 信口雌黄(Xìn kǒu cí huáng).