Why are the well-preserved cultural relics in the tomb seriously oxidized as soon as they are unearthed?

Like other bronzes, unearthed bronzes with different silver contents will be corroded by various chemicals during underground burial, which often leads to broken defects and reduced strength. If the unearthed bronzes are not protected and restored, it will not only be detrimental to the future research and protection of bronzes, but also affect the effect of the exhibition.