This is my first critique, so I'd love to know how helpful this is. Well, here it goes...
The thing I enjoyed most about the story is the characters. I felt like you did a good job of conveying each character's personality and motivations. I felt like I had a good distinct picture of who each person was, even the more minor characters. This drew me into the story the most, and was my favorite part.
The part I had the most trouble with was following the more technical parts. I didn't really understand what the philosopher's stone was, although I definitely got the idea that it was controversial. I also didn't understand the part about being faerie/teething, etc. I wasn't sure what exactly was going on with the nymph, in particular, although she was an interesting character to listen to. It was probably because I had trouble understanding, but I also felt sometimes like it was going a little too fast for me to keep up with. I wanted to have a little bit more space to understand what happened before going on to the next big thing.
I did feel like I got a good visual picture of what was going on, even if I didn't understand the specifics of it. The world was interesting to me, even if I didn't completely understand the details.