From Shell to Studio: How Medieval Craftspeople Used Snail Shells in and around Paintmaking

This article explores the multifaceted role of snail shells in medieval paintmaking and related crafts. While marine snails were primarily exploited for Tyrian purple dye, leaving vast shell middens that sometimes supplied lime production, the calcareous shells of both land and marine mollusks also served as practical raw materials for painting. Burnt shells provided lime for frescoes, plasters, and the widely used bianco di San Giovanni, while ground shell carbonate occasionally substituted for chalk or marble as a white pigment or extender. Archaeological evidence of aragonite microstructures in mortars confirms biogenic shell use, though identifying snail shell sources in manuscripts remains difficult. Beyond raw materials, shells were indispensable studio tools, functioning as ready-made palettes and containers for pigments and “shell gold.” Through textual evidence, archaeological finds, and scientific analyses, the article highlights how snail shells—whether as waste from purple dyeing, sources of lime, or workshop vessels—contributed to the material culture of medieval painting.