I found this great image online. you could just sense the paints thickness, he preached to let the paint retain the tracks of the brush. i have a little suspicion that as much as he squinted he would also blurred his vision with eyes wide open in order to eliminate the number of planes and detail, in order to see color mass and color variations. This is why i think he was among the greatest to capture flesh tones because he then was more able to see color by itself instead of color as the result of planes. Color as the result of planes tend to be less continuous, less harmonic, more fractal. While color as the result of color mass or color gradation as the result of a blurry vision tends to be more harmonious. another obvious hint would be that his portrait doesn't look sculptural like a modern day portrait that is so dependent on facial planes. Share your thoughts or your own revelations.