Why does lead oxidize during cupellation while silver and gold remain behind?

During the process of cupellation, lead is separated from precious metals because of its chemical reactivity compared to the noble nature of gold and silver.

When the impure metal is melted in a cupel and exposed to a blast of hot air, the lead readily oxidizes to form lead monoxide (PbO). Unlike gold and silver, which are highly resistant to oxidation and remain in their metallic state, the lead oxide is either vaporized or absorbed into the porous material of the cupel. This process relies on the fact that while lead acts as an effective solvent and collector for silver and gold during initial smelting, it can be selectively removed through oxidation, leaving behind the purified precious metals.12