大方廣佛華嚴經隨疏演義鈔 22.6

22.6

疏「經云：水銀和真金，能塗諸色像」等者，金如法身，水銀如般若，以般若照機，真身隨感故。天台智者亦用此義，以釋《法華》壽量應用。

Regarding the commentary's statement: "The sūtra says: Mercury combined with pure gold can coat all forms and images," and so forth: gold is like the dharmakāya, and mercury is like prajñā; because prajñā illumines capacities, the true body accords with responses. Tiantai Zhizhe also used this meaning to explain the responsive function of the [Tathāgata's] lifespan in the Lotus Sūtra.