Traditional science in pigments and recipe of painting woodcarving in medieval Assam, India

A painting tradition of medieval Assam, popularly known as Hengul-Hāitāl, has been studied with an aim of restoring and conserving centuries-old woodcarvings and Sāncipat manuscripts for preserving in ordinary open conditions at villages and Vaishnavite monasteries. The pigments, their combinations for producing various shades and the resulting colors have been characterized using various physicochemical techniques. The study unravels some interesting traditional science, such as, using red Hengul (cinnabar), yellow Hāitāl (yellow orpiment) and blue Nīl (Indigo or Prussian blue) as primary colors to produce any desired shade, inclusion of either or both of Hengul and Hāitāl in every shade to repel fungi and insects, applying Kharimāti (a clay) as a wood-primer for better painting effects, choosing of Bael gum as a robust non-staining natural adhesive and finally varnishing with Lā (a natural lac) to protect the pigments from natural erosion and protect the woodcarving from humidity and contaminating hands touching them. The findings provide clues to develop an appropriate method of restoration of partially worn-out woodcarvings for preserving them in ordinary open conditions, based on the traditional method of preparation.