Black, made of rubber, coreless, hilt looks like a spine, pommel is a skull, and if you hold it under a bright light you may see I have used marker pen in the eyes giving them a sheen (it was a black marker I think but under bright light may have a faint purpley tinge to it).

Lost in the Caves on 24th Aug 14. Probably in the area you get to via the bog blocks then turning right (near the room with the massive boulder which you enter via a bridge).