What drains out of Tom Riddle's diary in the Chamber of Secrets?

My mom and I were watching Harry Potter: Chamber of Secrets last night. In the scene where Harry destroys Tom Riddle by stabbing his diary with a basilisk fang in the Chamber of Secrets, my mom thought that the dark liquid that spurted out of it was blood. I said it was ink that was built up in the pages. Who do you think is right? Please let me know!