If you saw black on the pad after. Then maybe you didnt pre burn the crap off the pad before placing the pad in the pipe. It is important to burn the machine grease industrial chemical they put on the pad. Very simple. Take the pad with something like tweezers, scissors or pliers and hold it and burn the pad with a torch lighter until it is burning red. Do this outside because it will smoke a bit and smell nasty! Then wash it and let it dry, then it is ready to place in the pipe and load it up with spice!

Good luck! 

EDIT: I heard that soaking in alcohol gets rid of the nasties but doesnt tarnish like heating does. So you learn something new every day!