In the x-ray it was possible to see that the overall state of the work is generally good. In addition, it revealed small corrections made during the process of execution: Rubens modified decorative elements of the horse, the fall of the King’s cloak and the face of the angel representing Victory (fig. 1). Such a direct manner of execution can perhaps be explained by the fact that Rubens was basing himself on pre-established iconographic models due to the posthumous nature of this portrait and perhaps in response to the patron’s requirements. These sources would have helped him when organising the composition. Furthermore, we know that the artist looked to the equestrian model of Charles V in Cornelisz. Vermeyen’s tapestry and that he copied the face from Philip II in Armour by Titian.

The dimensions of the canvas prior to restoration (314 x 228cm) did not correspond to the original size of Rubens’s painting (247 x 223cm), which had been enlarged in the 18th century, principally at the upper and lower edges. By analysing the area where the additional pieces of canvas joined the original one it was possible to appreciate different radiographic densities and different craquelure which clearly indicated the edges of the preparatory layer and the paint of Rubens’ original work, thus indicating the original dimensions of the painting (fig. 2).

In the micro-samples taken from the two added strips, the preparation is red and not grey-brown in colour and is basically made up of red earth and variable amounts of white lead. The proportion of white lead is greater in the upper strip than in the lower one, due to the fact that the painter/restorer wished to give the sky a lighter base tone. The materials used in the preparation of both added strips are the same, allowing for the conclusion that they were added at the same time (fig. 3).