Pu yu hun jin
This can mean a person of excellent character but ordinary appearance (like the English idiom “diamond in the rough”) or more literally an object of great value with an unassuming appearance.
Shan Tao was one of the “Seven Noblemen of the Bamboo Forest.” He was well known for his noble character and upright conduct as an official. There was a man whom he greatly esteemed named Ji Kang, whom he recommended for an official post. However, Ji Kang did not appreciate this at all, and in fact broke off relations with Shan Tao when he learned of it.
Later Ji Kang was attacked and killed by the Sima clan. Unafraid of the Sima clan and their allies, Shan Tao stepped in to care for all the members of Ji Kang’s family.
After the establishment of the Jin dynasty, Shan Tao was placed in charge of decisions regarding the examination, selection, assignment and transfer of all officials in the country. He held this post for a long time and took his responsibilities very seriously. The success or failure of the men he chose to govern the country were reflected in the citizens’ appraisal of Shan Tao himself.
At that time there was a certain county magistrate who plundered the wealth of his county without restraint. Fearing that one of his subordinates would accuse him, he attempted to gain Shan Tao’s favor with a bribe of a hundred jin* of silk. So as not to reveal the difference of character between himself and others, Shan Tao received the silk without emotion, but ordered his servant to seal it in an empty room and not allow anyone to move it. Later, when the county magistrate was found out, many other officials were implicated in his crime and interrogated. When enquiries reached Shan Tao, he revealed the pile of silk rolls. The investigators saw that the top rolls were covered in dust and the rolls underneath had not even been touched. Shan Tao’s reputation spread even further.
One of the other “Seven Noblemen of the Bamboo Forest,” Wang Rong once wrote in praise of Shan Tao, “如璞玉浑金， 人皆钦其宝， 莫知名其器.” (Literally: “Like rough jade impure gold, people all venerate his preciousness, not one knows his utility.”) His meaning was that Shan Tao was like jade that had not been shaped or gold that had not been refined. Often, people only admire the brilliant appearance of gold or gems but do not know the inner quality of gold or jade that have not been cut and polished.