I've just been thinking about random HP things, as one does, and I was hoping ya'll could clarify a point about Pensieves for me.

My question is: When you are putting a memory into the pensieve for viewing, is that silvery stuff the actual memory, or just a copy? For example, if Harry decided to view the Sectumpsempra incident, and took out the memory, would he still have any recollection of the memory BEFORE looking at it again?

ETA: And if it is just a copy of the memory. Do you think this memory copying spell can be applied an unlimited number of times? Could Harry withdraw/copy that Sectumsempra memory multiple times, without any degradation? Would it being copied affect the original memory, or just dilute the copy?? I'm over-thinking this.