So far as is known to the writer, the only published studies of this subject are one by himseIf, made many years ago, and a more recent one by Professor André Pochan, though references to the appearance and colour of the stones are not uncommon. Thus both Jomard (who climbed the pyramid) and Maspero (who apparently did not climb the pyramid, but relied upon Jomard's description) both say that the portion of the casing of the pyramid of Chephren, still remaining in place at the apex, is coloured reddish in patches by lichen, the identification of this apparently having been made by the well-known botanist Delile, who accompanied Jomard on his climb up the pyramid.
Professor Pochan, who also climbed the pyramid of Chephren, 2nd examined the stones at the apex, states that he saw lichen, but only on the north side, where the colour was blackish, and that the stones in general are of a reddish-brown colour. No proof that the black was indeed lichen is given, and the very dry situation would seem to make the presence of lichen improbable, unless it is growing on the patches of bird excrement that Jomard noticed, which, however, are not likely to be confined to the north side.