Thank you for the feedback, I know about clue variations, though one is definetly missing. Last night I couldn't sleep, so I thought I'd search some more. A total of one hour later I have concluded that the clue is not in my scene at all.
I was looking for the fifth clue in Glassmaker Act 5, reviewed a couple of guides aswell, but I hadn't found the 5th clue, which should be a pile of glass shards, near some Glassmaker Ointments. It is probably a glitch, because I have been looking for it for nearly half an hour now. If you could help, it would be greatly appreciated. -Matt