It should be that the fake gold should be plated with real gold. If the real gold is not gold-plated, the direct translation is that only fake gold needs to be plated with real gold to cover it up. Real gold does not need to be gold-plated at all.

This sentence is used to satirize those who have no real talent and practice deception. If a person is really talented, there is no need for any academic qualifications or other things to modify it. If it is real gold, it will shine.

As for the source, you can refer to the following.

The origin of the word "gilding" originally refers to the scene of geishas putting on makeup in the Tang Dynasty

Bai Juyi's "Xiliang Geisha" of the Tang Dynasty said: "The carved wood is the head silk and the tail is gold. "Gold plating" describes the scene of geisha putting on makeup. Later, Zhang Xiaobiao, a poet from Qiantang, failed to pass the imperial examination several times and went on a snowy day to relieve his boredom. Later, after Zhang Xiaobiao was persuaded by Huaidong Jiedu envoy Li Shen, he worked hard for ten years and passed the exam. He happily wrote a poem: "When he came first, he defeated all ten political officials, and the golden soup came out of Chang'an. The horse's head gradually entered Yangzhou Guo, washing the eyes of the time teller." He sent this proud poem to Li Shen. Li Shen saw Zhang Xiaobiao's arrogance and magnanimity from the poem, and wanted to educate him, so he wrote a poem "Answer to Zhang Xiaobiao": "Fake gold should be plated with real gold. If the real gold is not Gold-plated. Chang'an has won the first place in ten years, so there is no need to be high-spirited on an empty stomach." Zhang Xiaobiao was greatly ashamed when he saw this poem.