Most of the material presented is drawn from the Bavarian State Collections. Diagrams of the make up of supports are given including some 35 uncradled oak panels. On 14 supports brands were found and the incised initials, MV, of Michiel Vrient the Antwerp panel and frame maker who frequently supplied Rubens. The Rainbow Landscape bears the initials NV, presumably of his son and successor. As the father died in 1637/8 this suggests rather a late date of origin of this painting which on stylistic grounds is considered a copy after the much larger panel in the Wallace Collection. This corresponds with the dendrochronological results. Rubens's frequent practice of first starting with the smaller central portion of a composition and subsequently adding on to it is illustrated by the Drunken Silenus , the small Last Judgment and two portraits of Helene Fourment. After return from Italy R. developed his characteristic streaky gray priming in an aqueous medium which breaks the monotony of the white chalk grounds on panel and not only creates an illusion of space but also imparts a vibrating luminosity to the more thinly applied passages of the superimposed paint layers. The color of the grounds on canvas supports varies from a light brown to a light grey. In the majority of cases a two layer system was found: 1) light orange-brown ground of a mixture of various ochres with lead white and additions of chalk in an oil medium (100-250 mu), 2) a rather opaque top layer of lead white and charcoal black in an oil medium (15-50 mu). This double priming apparently provided sufficient variety within the predominantly light grey grounds. Rubens frequently drew his very first compositional ideas not only on paper but directly on the primed wooden support of his sketches; soon however he would switch from the pencil to brush and oil paints which had the consistency of water colors. Where this brush drawing is used exclusively it merges perfectly with the superimposed coatings. A survey is given of the different types of preparatory oil studies employed by Rubens for his final compositions. Reference is made as to their functions inside and outside the workshop where numerous hands participated in an unprecedented production of paintings and designsfor tapestries, engravings, etc. A fine oil sketch with The Conversion of Saul by an unidentified pupil of Rubens served as a modello for a stained-glass window, as the particular type of incised graticulation suggests.