Leather was an important commodity for the British empire in terms of industrial production and scientific innovation. From the mid nineteenth century in India, the British sought to convert leatherwork into a scientific industry. Leather, however, also has a life in caste. The profound stench inherent to the process of leather tanning marks leather workers as polluted. Examining archival material and contemporary ethnography from Uttar Pradesh, this paper examines how the scientific colonial intervention in leatherwork was made complicated due to the sensorial politics of caste. The leather chemist, trained to impart scientific knowledge to leather workers, often failed to negotiate the caste-based sensorial nature of leatherwork, thereby allowing caste to limit the reach of modern science in the industry. Understanding this interaction between colonial science and leatherwork has important consequences for our understanding of the politics of caste and scientific knowledge in India.