I recently commissioned photography of Mr. Pitt's death mask. It's in safekeeping at the Chevening Estate near Sevenoaks, Kent. Although I'm not a fan of death masks, in the obvious absence of any other accurate means to ascertain what William Pitt actually looked like, the mask is all that is left.
Reading William Beckford's memoirs, however, make me slightly apprehensive to see it. There is a passage which describes the death mask, and it physically turns my stomach:
"Pitt died under great bodily suffering, if the mask taken from his face immediately after death be any indication of it. In general, death removes all traces of living agony, and the features assume a remarkable placidity, but it was not so here. Mr. Beckford stated, that calling upon Nollekens, the sculptor, just after Pitt's decease, he showed him the cast from his face taken just after he died. It was so horribly distorted - so frightful, apparently from pain, that it was not of the smallest use for the work which Nollekens was about to undertake. "It almost scared me," said Mr. Beckford; "there were no traces of my old and early acquaintance. The mask was fearful to look upon" (pp. 318-319).
Beckford, W. (1859) Memoirs of William Beckford of Fonthill (Vol. 2). London: Charles J. Skeet, pp. 318-319.