The hand of the connoisseur: Gems and hardness in Enlightenment mineralogy

Historians of natural history have shown that the study of plants, animals, and minerals was a form of connoisseurship in the eighteenth century. Historians of early modern experiments have linked scientific knowledge to the manual skills of artisans. I combine these two insights, arguing that connoisseurship in the sciences meant learning to touch, not just learning to look. The focus is on gems and mineralogy in eighteenth-century France. I show, firstly, that the study of gems was linked to the connoisseurship ("connoissance") of paintings. Next, books on gems were closely related to the new mineralogical treatises that emerged in the middle of the eighteenth century. These treatises formalized a distinction between "Oriental" and "Occidental" gems that was also a distinction between hard and soft gems. The best judges of hardness were gem cutters, a group that participated in mineralogy through the culture of collecting. Finally, the knowledge of cutters contributed to the quantification of hardness in the form of the hardness scale and the scratch sclerometer.