Why did ming china demand that europeans pay for goods with gold or silver?

Ming China (Or the Ming Dynasty from 1368 to 1644 A.C) demanded that Europeans pay for goods (as silk and porcelain) with gold or silver, because the Chinese didn't want any product that the Europeans could offer as exchange, due to that the silks and porcelains the Chinese produced were more valuable than the spices, wool and linen that the Europeans used to produce, and also the Chinese didn't need that products because they used to make them themselves.