"Dumbledore’s innumerable contributions to the state of Wizarding knowledge, including his discovery of the twelve uses of dragon’s blood, will benefit generations to come, as will the wisdom he displayed in the many judgments he made while Chief Warlock of the Wizengamot."
-- passage from DUMBLEDORE REMEMBERED by Elphias Doge (DH2)
The “Twelve Uses of Dragon’s Blood” is one of the most important discoveries made by Albus Dumbledore during his lifetime. It was mentioned on his chocolate frog card (PS6) and in an article memorializing him after his death (DH2). One of the uses is oven cleaner (SFC). Another is reported to be spot remover (LA Times interview with Steve Kloves).
Q: What are the 12 uses for dragon's blood?
A: I have a very good reason for not telling you -- the movie script writer wants me to give him that information for the film. But I can say that the 12th use is oven cleaner (SFC).
In an interview with the LA Times, scriptwriter Steve Kloves said:
What kind of things do you run by Rowling?
A range of things, even something really simple. I once asked about the 12 uses of dragon’s blood, which is referenced in the books. There are writers who would write “12 uses of dragon’s blood” and not have a clue what they are; it just sounds cool. But I emailed her to ask (and this was 10 years ago), and 25 seconds later I get an email back with a list.
Do tell. Shes only mentioned oven cleaner in interviews.
One is an oven cleaner, yes. Another is a spot remover. . . . It was really amazing. Really, the books are only the thinnest surface of what she knows about the series. Where Jo is helpful in a more serious way for me is when I want to know more about motivation or background, when Harry realized certain things, when characters understood things. There was one case where I was violating a plot thing it had something to do with Dobby, I think and she said, No, you don’t want to do that, as she knew what was to come. She’s a great resource for problem solving and she has such a facile mind, she can help with complicated things. Though her plots are so fiendish that they’re really difficult for cinema.