Abstract
<title>Abstract</title> <p>The Mogao Grottoes house over 2,400 polychrome clay sculptures whose painted surfaces are slowly damaged by shifting temperature and humidity, yet a statue's decay under a given climate cannot be predicted.We present a digital twin - a living virtual replica of a sculpture - combining models of five decay processes (colour fading, mould, salt damage, cracking, and ageing) and rendering their effects on a 3D scan under any future climate.Built with Model-Driven Engineering, the framework is generic and reusable across objects and sites.To ground the fading model we aged mineral-painted replicas of traditional Dunhuang clay for two months; this pilot gives the first controlled fade-rate contrasts, with vermilion, azurite, and malachite ageing 1.5 - 2 timex faster in the cooler, humid arm.Under its own stable climate the sculpture should change little; the twin's value is the counterfactual - how fast decay would accelerate if control were lost - guiding preventive care.</p>