Possible Clues:

• The 'Dark Side of the Moon' cover has one
• Rainbow creator
• Light-splitting glass
• Polyhedron
• Gentleman getting up in the afternoon -- the object's transparent!
• Transparent object that refracts light
• Glass shape splitting light into a spectrum
• Cut-glass object teacher put up in the course of the afternoon
• Crystal form
• It separates a beam of white light into colours