white. Jean de Berry owned 19, while Mary of Burgundy, Isabella of Valois, Isabeau of Bavaria and Philip the Good all held substantial collections. Tapestry production began with design. The designs, or cartoons were typically executed on paper or parchment, put together by qualified painters, then sent to weavers, often across a great distance. Because cartoons could be re-used, craftsmen often worked on source material that was decades old. As both paper and parchment are highly perishable, few of the original cartoons survive. Once a design was agreed upon its production might be farmed out among many weavers. Looms were active in all the major Flemish cities, in most of the towns and in many of the villages. Looms were not controlled by the guilds. Dependent on a migrant workforce, their commercial activity was driven by entrepreneurs, who were usually painters. The entrepreneur would locate and commission patrons, hold a stock of cartoons and provide raw materials such as wool, silk, and sometimes gold and silver – which often had to be imported. Entrepreneurs were in direct contact with the patron, and often went through the nuances of the design at both the cartoon and final stages. This examination was often a difficult business and necessitated delicate management; in 1400 Isabeau of Bavaria rejected a completed set by Colart de Laon having earlier approved the designs, to de Laon's – and presumably his commissioner's – considerable embarrassment. Because tapestries were designed largely by painters, their formal conventions are closely aligned with the conventions of panel painting. This is especially true with the later generations of 16th-century painters who produced panoramas of heaven and hell. Harbison describes how the intricate, dense and overlaid detail of Bosch's Garden of Earthly Delights resembles, "in its precise symbolism ... a medieval tapestry". Triptychs and altarpieces Northern triptychs and polyptychs were popular across Europe from the late 14th century, with the peak of demand lasting until the early 16th century. During the 15th century, they were the most widely produced format of northern panel painting. Preoccupied with religious subject matter, they come in two broad types: smaller, portable private devotional works, or larger altarpieces for liturgical settings. The earliest northern examples are compound works incorporating engraving and painting, usually with two painted wings that could be folded over a carved central corpus. Polyptychs were produced by the more accomplished masters. They provide greater scope for