"Sicut crystallus quando est obiecta soli": rock crystal, transparency and the Franciscan Order.

This essay investigates the artistic applications and the significance of rock crystal (transparent quartz) in Western Europe in the thirteenth and fourteenth centuries, when the demand for transparent and translucent artistic materials increased and newly-developed devotional and liturgical practices enhanced the significance of vision and visibility as a means to access and comprehend the divine.The first section of this article explores issues of sourcing and trading of rock crystal, also introducing the techniques available to carve this stone during the Middle Ages. The second section engages more directly with the meanings of transparency, examining a group of liturgical rock crystal crosses that were manufactured in Venice, were widely exported throughout Europe, and were particularly popular within the Franciscan order. This essay argues that the aesthetic qualities of rock crystal were especially compatible with the ideals of austerity promoted by the Franciscans and that they concurred with the interests of the Order in questions of physical and spiritual vision, and mystical access to God. As the rudiments of the debates on the nature of light conducted by Franciscan scholars were disseminated outside academic circles, the functioning of physical and spiritual seeing and the affective and transformative powers of vision became a major concern of Western Christendom – contributing to explain the widespread popularity of rock crystal and other transparent and translucent artistic materials at this time, as well as the nature of the aesthetic experience of late medieval beholders.