In his own clever words on his website he explains he thought art an attempt to reveal the secret that was hidden behind appearance:

"Thus, he constantly tried to depict the human face because he considered it the key to understanding the person and a way to question his or her secrets and inherent potential. This could be carried out through capturing the details of the face in a process that combined drawing and erasing. It resulted in an abstract face, not in the usual sense of abstraction, but in the sense of denying the details that were not relevant to the notion that the artist wanted to capture. The artist focused only on the meaningful fragments, which were the expression of the world that he was trying to depict."

Hence the editors of this dictionary come to the conclusion that the excellent painting to the left by Diaz in the best tradtition of the Italian renaissance is not H.M. King Faisal but an abstraction of Diaz. (2008).