Is This Mold On An Older Canada Mint Stamp?

This is Canada 1897 Queen Victoria 'Leaf' Issue Scott #72.
I have not had much experience with mint stamps, especially older ones.

I noticed that there seems to be blackish smudges or spots on the back of this stamp. Also the gum is cracked? bent? and missing in some places around the edges.

I am worried that this black is mold or something. I think I remember reading something about spotty or moldy stamps on here somewhere but didn't pay attention at the time as I had not seen anything like it before. Is this that? Or what could it be? Dirt?

If it is mold is there a way to clean it or make it better?
Thank You!