The surface paint layer of the triptych (1432) was subjected to a stereomicroscopic examination of existing and new cross sections in June of 1986; in addition to this work, microchemical stain tests, immunofluorescence (for binder identification), ultrasound, and x-ray diffraction analysis (for identifying mineral pigments), thin-layer chromatography, gas chromatography, and high performance liquid chromatography were performed for this study. The colors studied were blue (azurite, ultramarine), green (copper resinate), yellow (iron oxide), and red (vermilion, lake). The results are reported and compared with earlier studies of van Eyck's painting technique.