The wood grain and panel join are evident in the x-ray image in the centre, and nail holes from a past framing method can also be seen. The unusual mottled appearance of the x-ray is likely due to the manner in which the priming layer was applied. The face is painted with soft blended brushwork and the costume detail is carefully executed. The underdrawing seen in the infrared reflectogram on the right clearly derives from a pattern, with short carefully placed lines marking the shape of the beard and areas of shadow.
© National Portrait Gallery, London