信口雌黃

「雌黃」是一種黃紅色的礦物。古時候的人寫字用黃色的紙，寫錯了都用雌黃塗抹。

晉朝時候，有一個叫王衍的人，他年輕的時候，口才就很好。後來他在政府機關做事，更是常常引用他讀過的「老子」、「莊子」中的道理，到各處講演，講國家大事。因為他講得很詳細，又隨時加上自己的看法，所以人人都聽得懂。在那個時候，他已經是很有名的演說家了，大家都很佩服他。

王衍在很多人面前講演的時候，總是不慌不忙，有時候把內容講錯了，就很從容地隨口改正，於是人們說他是「口中雌黃」。

Randomly Speaking Out Orpiment

"Orpiment" is a kind of reddish-yellow mineral which was used in ancient times to paint over mistakes one made when writing.

During the Ch'in dynasty, there lived a man named Wang Yan, who was very eloquent. Wang Yan worked for the government, and would often travel from place to place lecturing the affairs of the country. His lectures were very thorough, and he also added in his own opinions, so his audience always understood him, Wang Yan was a very well-known lecture, admired by everyone.

Whenever Wang Yan gave a lecture, he was always at ease and unhurried. If he made a slip of tongue, he would calmly go back and correct himself. Therefore people said that the "had orpiment in his mouth".

People of later generations expanded this idiom. Randomly saying things for which one has no proof is now known as "randomly speaking out orpiment."