In this non-technical article, the author furthers the knowledge of Jan van Eyck's artistry and working methods by a study of the underdrawings and changes of composition revealed by infra-red photography. The underdrawings are shown to be elaborately detailed. On the basis of this observation, the author concludes that the Antwerp drawing on panel of St. Barbara is not a finished drawing, but a <i>préparation for a painting. Changes of composition are found to be numerous. Many of these changes, especially in portraiture, seem to be modifications of drawings-from-life for aesthetic reasons. -- AATA