Both these articles deal with Ghost in some detail. There are references to trace – making traces solid.
What is interesting is that the traces are in the walls and the cast of the space creates a mould of the trace, but a cast of the space.
Theses casts seem to hover between positive and negative, like a daguerrotype.
Also deals with positive and negative spaces, the body, casting etc.
links Whiteread with spirit photography..