An introductory survey is given of the foremost trends in Antwerp painting before Rubens in order to specify the technical problems encountered by Flemish mannerists trying to master the Italian chiaroscuro with their own traditional workshop principles: enamel-like purity and translucency of color. Attempts to impart more density to their figures diminished those qualities and resulted in obsure shadows and rather opaque colors. Mostly the paint is applied too thinly in the lights which tends to harden the modelling while the transitions to the shadows lack subtlety (F. Floris). Guided by Venetian painting Marten de Vos uses vivid colors of greater density on top of the familiar Flemish chalk ground and underdrawing but they lack the essential qualities of rich oil paint required for a more simplified technique developing towards a one-phase operation. While in the South Rubens gradually took to the Italian methods and made use of the colored grounds. He worked from dark into light and increased the thickness of his paint layers. His color and technique were greatly influenced by Venetian practice and above all by Titian whose works he frequently copied. Back in Antwerp Rubens reverted to his native tradition. He gradually succeeds in integrating tonal principles of paint application in the Venetian manner with the Flemish principle of creating transparency on the basis of a luminous ground. In the Crowning of the Hero of Virtue his apparent efforts aimed at a mother-ofpearl-like effect of the flesh painting created by combining pink, yellow and bluish color blended together in an enamel-like paint application of greatly varying thickness. Even without varnish this paint surface has a slightly glossy surface in most parts which accounts for a well-balanced medium on the basis of a drying oil. There is analytical evidence that in background areas of dark brown color Rubens used oil-resin as well as tempera. In the Cupid pointing his bow Rubens has carried his experiments in flesh painting to full perfection. He also makes use of the turpid medium effect in his distinctly bluish halfshadows which in this particular case do not contain blue pigment. At this stage of his artistic development there is ample evidence that he systematically employs the three primary colors and that he might have exchanged ideas with contemporary scientists theorizing on optics. Reference is made to these sources as well as to Rubens's critics of later periods in regard to his use of color. Detailed observations in the Hippopotamus Hunt give evidence of the functions of local underpainting in a broken white and of the extensive use of transparent paint and finishing glazes. This large size painting also impressively demonstrates the economy of Rubens's technique in areas such as the extensive frontal view of the rearing horse where oil paintingand drawing techniques are closely related. Very likely in this case a drawing served as the preparatory study. A short account of pigments and their characteristic mixtures as they frequently occur in Rubens's paintings is given. There is evidence that mixed green colors were often prepared with tempera. The section on media provides references to the De Mayerne manuscript and to Rubens's correspondence. It also covers the renewed interest in the mystified medium since 1850 as a source of inspiration for artists' technique and modern commerical production. First results of a continuing binding media research program at the Doerner-Institute (by F. Preubetaer) confirmed the occasional use of tempera in addition to oil. There is little evidence so far to support the widespread view that Rubens generally used oleo-resinous vehicles.