37

Now we all know that it had been established in book one and confirmed again in book seven that Gringotts is not a place to mess around with unless you are a really skilled or very accomplished Dark Wizard.

For instance, while going to the Lestrange's vault in the hope of finding a Horcrux, the bank cart was forcefully passed through the Thief's Downfall, a sort of magical waterfall which wipes out all magical enchantments, thus making the thief extremely vulnerable and prone to easy capture by the guards.

Now the funny thing is that, while the effect of Polyjuice Potion was removed from Hermione and Ron, Hermione's enchanted purse didn't burst open after going through the enchanted water.

Why did this happen? Any theories?

45

The relevant quote from the book:

“The Thief’s Downfall!” said Griphook, clambering to his feet and looking back at the deluge onto the tracks, which, Harry knew now, had been more than water. “It washes away all enchantment, all magical concealment! They know there are impostors in Gringotts, they have set off defenses against us!”
Harry Potter and the Deathly Hallows, Chapter 26, Gringotts

Hermione, hearing this, instantly checks her bag:

Harry saw Hermione checking that she still had the beaded bag, and hurriedly thrust his own hand under his jacket to make sure he had not lost the Invisibility Cloak
Harry Potter and the Deathly Hallows, Chapter 26, Gringotts

We know from the beginning of the chapter that Hermione had tucked it away safely

It was now packed inside the beaded bag, which, Harry was impressed to learn, Hermione had protected from the Snatchers by the simple expedient of stuffing it down her sock.
Harry Potter and the Deathly Hallows, Chapter 26, Gringotts

Here is the key moment that answers your question:

she pointed Bellatrix’s wand at the waterfall and cried, “Protego!” They saw the Shield Charm break the flow of enchanted water as it flew up the passageway.
“Good thinking,” said Harry. “Lead the way, Griphook!”
Harry Potter and the Deathly Hallows, Chapter 26, Gringotts

Conclusion

The waterfall has to actually touch the enchanted object (in the case of the Polyjuice potion effects, it washed over the people). From Hermione checking for her beaded bag, we can assume she had it safely tucked away and it didn't get washed by the waterfall, and then they used her Shield Charm to break the flow of the waterfall and get away without it being washed.


Alternate ideas and conjecture

Early on in the Deathly Hallows book, we are introduced to the beaded bag, and are fed a potentially key (to this question) piece of information

to Harry and Ron’s utter astonishment, she pulled out a pair of jeans, a sweatshirt, some maroon socks, and finally the silvery Invisibility Cloak.
“How the ruddy hell — ?”
Undetectable Extension Charm,” said Hermione. “Tricky, but I think I’ve done it okay; anyway, I managed to fit everything we need in here.”
Harry Potter and the Deathly Hallows, Chapter 9, A Place to Hide

We have very little canonical information, evidence or basis to make any assumptions about Goblin magic, but it's possible that Hermione's Undetectable Extension Charm on her beaded bag made it so the Thief's Downfall didn't detect (and therefore didn't wash away) the extension charm.

That being said, Griphook assures us that it washes away "all enchantment, all magical concealment", so we have, both, the mystery of Goblin magic and Griphook's word working against us in this hypothesis.

  • 1
    Thank you. I forgot about Hermione performing the shield charm :) – Harry Nov 28 '16 at 13:42
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    This seems like a very ineffective security device if all a thief has to do to bypass it is wear a raincoat. – Bradley Uffner Nov 28 '16 at 15:44
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    @BradleyUffner They probably bank (pun not intended) on mystery. Even with Griphook the trio were never informed to wear raincoats prior to the heist. – Ghoti and Chips Nov 28 '16 at 15:47
  • 9
    @GhotiandChips that's called security by obscurity and generally speaking, it's not very effective. – stannius Nov 28 '16 at 20:22
  • 1
    @stannius: In this case, it has to work only once (which it did), thus Security by Obscurity was working here... – arc_lupus Nov 28 '16 at 23:00
11

It is possible that it is because the undetectable extension charm is not considered concealment. Remember that in the sixth book Hermione points out that secrecy sensors do not work on everything. She notes that a potion in the wrong bottle is not considered a dark object. Likewise, the undetectable extension charm is considered a charm to give you more room, not a charm to conceal all the stuff in your bag.

Note that the undetectable extension charm provides ZERO protection to the items inside. Unlike moody's magical trunk, all of the items inside the bag are easily accessible, as Harry is able to access all the items inside while looking for dittany. The bag also does not prevent spells being used on the objects, as Harry ends up using a summoning charm on that same dittany. Also notice that Hermione does check to see if the bag is okay. She is unsure what will count as concealment too. I guess they just got lucky that undetectable extension doesn't cut it as a means of concealment.

Conclusion: The bag is just not conceal-y enough to count.

  • 2
    Fair enough fan-theory, but then what'd be the point of Hermione breaking the flow of the waterfall with her shield charm? What'd be the point of her checking her bag in the first place? – Ghoti and Chips Nov 29 '16 at 0:22
  • I always assumed it was because he still needs Bogrod. The imperious curse lifts when they go through the water. Since they still have to go through with Bogrod in tow, they need to keep the water off of him. – EvSunWoodard Nov 29 '16 at 15:29
  • @GhotiandChips - Also, as I said, she is checking her bag because she doesn't know whether or not it will be affected. It turns out to be safe, but she doesn't know that until after. – EvSunWoodard Nov 29 '16 at 15:31
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    @GhotiandChips - I'm starting to worry you aren't reading what I'm writing. I think you are confusing "undetectable extension charm" with "undetectable, extension charm". The idea is that you can't detect that the bag has been extended from the outside, NOT that you cannot detect what is inside the bag. The bag is not designed for concealing items, which is why Harry can freely retrieve items from inside it, unlike Moody's trunk, which actively hides the contents. Therefore, the falls don't consider it a concealment charm, but a handy, space-saving charm. – EvSunWoodard Nov 30 '16 at 15:04
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    What I'm saying is that some canonical magic is intent based. A secrecy sensor (a device which detects secrecy) does not react to a love potion in a different bottle (aka a hidden potion). So, it is not a reach, that the thief's downfall will not detect the extension charm. Because the point of the spell is to make more space in a confined area, the point is NOT to conceal what is inside. Therefore, like the bottled potion, the extension charm is not counted. Magic does not care about the name of other spells, only what they do. I don't know what else could be confusing you. – EvSunWoodard Nov 30 '16 at 18:06

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