The right-hand image, taken in ultra violet light, reveals extensive retouching, visible as dark spots over the varnish. The x-ray in the centre shows damage to the right of the face. The wavy and irregular wood grain of the support is also clearly visible, while the seal on the back of the panel can be seen as a white circular shape in the face. The modelling of the sleeve can be seen more clearly in the x-ray than in normal light because lead white, which blocks the x-rays, increases the contrast between grey and black.
© National Portrait Gallery, London