Information related to the technical examination of the oil sketches for Rubens's Achilles Series are presented. The streaky imprimaturas used by Rubens are described. Underdrawing was found on some of the panels. In one case, it is described as applied over the streaky imprimatura. The underdrawing material analyzed was identified as black chalk, made from carbonaceous clay stone. The binding medium of the imprimaturas was analyzed using Fourier transform infrared (FTIR) and direct temperature-resolved mass spectrometry (DTMS). The medium was identified as egg with a possible small addition of oil.
