Organic colourants have been widely used in global cultural heritage. This project will examine the possible effects of solvents on the solid-state structure of a historically important crystalline organic pigment. Piuri, often referred to as Indian Yellow or gaugli among other names, is a vibrant yellow-orange pigment widely used in Pahari period paintings (17th – 19th centuries) and Rajput-Mughal paintings (16th – 19th centuries) in a variety of media from manuscripts to wall paintings. The pigment, along with imitations and adulterated material, was also exported and used by artists in Europe, such as J M W Turner. Indian Yellow is unusual in that its primary constituents are crystalline organic materials. In this project you will investigate the solid-state structures of the components of Indian Yellow through the synthetic production and characterisation of each substance. You will develop skills in crystallography, synthetic organic chemistry, and gain an understanding of how conservation science can support the conservation of art. Supervision at NTU will be provided by Dr Joshua Hill and Dr Warren Cross and conducted with partners who work on the conservation of objects and sites containing Indian Yellow as well as support from external collaborators in computational chemistry. The origin of Indian Yellow, which was not produced after the nineteenth century, has been long disputed and extensively investigated; recent work supports the hypothesis of production through processing and concentrating urine from cows [Ploeger 2019]. Existing analytical observations and computational work point towards the possibility of the presence of different solid forms of Indian Yellow, i.e. the possibility of polymorphism [Martin de Fonjaudran 2017]. In art conservation it is common to use a variety of solvents for certain interventions, such as cleaning, and collections may be exposed to other small organic pollutant molecules in museum environments. Many comparable organic solids are known to undergo changes in solid structure on exposure to such solvents and in this project you will investigate such mechanisms in Indian Yellow. The project will also contribute to synthetic methods for the production of xanthones, which are of wider interest for their bioactivity.
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