Dambulla Cave Temple tempera frescoes: clay-straw under-plaster and mineral pigment stability?

The monumental rock-ceiling murals of Dambulla Cave No. 2 (Maharaja Vihara) cover over 2,000 square meters of concave granite bedrock. Ancient painters prepared the rock by applying an underlayer of alluvial clay tempered with chopped paddy straw, crushed termite mound earth, and finely shredded cotton cloth rags to buffer thermal expansion. This was skimmed with a 2mm finish coat of slaked shell lime blended with jaggery water and boiled Beli fruit mucilage (Aegle marmelos). Pure mineral pigments—cinnabar for vermilion, orpiment for yellow, lampblack for outlines, and green earth—were bound with plant gums and applied secco onto dry plaster.