harry potter - Did the creators of the Marauder's Map rediscover lost magic?

Specifically, I'm thinking of the Deathly Hallows and their age.

I have a vague memory of either Ron or Hermione commenting on it being unusual that Harry's Invisibility Cloak has worked so well for so long, that the magic normally fizzles out after a few years, once the heard the story about the Deathly Hallows.

What I don't remember was how specific it was to that type of magic.

Should the magic used in creating it have worn off over time? Offhand, all I can think of that couldn't have been renewed regularly are the horcruxes and their protections - which may have just been powered by the piece of soul in them.

If it should have worn off, did (at least one of) the creators of it figure out how to make the magic permanent, like the Deathly Hallows are?

Answer

There seem to be two sides to this coin, there are some examples of magic wearing out after a period of time, and several examples of magic not wearing out after a period of time. The Marauder's Map seems to fall into the latter of these categories, presumably lasting for generations to come.

Examples of magical items that wear out after a period of time include:

• Most: Invisibility Cloaks


• Some: Wands (see Ron's borrowed wand from Charlie).


• Most: Brooms (see school brooms, and again the Weasleys)


• Special cases: Professor Slughorn tells Harry that when Lily Potter died, the enchanted fish that she gave him as a present also vanished. Additionally, when Dumbledore dies, the spell that he has on Harry also stops. This does not seem to be the case with the Marauder's Map however, as it is still working at the end of the series (according to JKR) despite all of its creators being dead.

Despite these examples though, the majority of items seem to maintain their spells, and in fact quite a lot of items seem to increase in magical power with age, kind of like aged wine:

• Most: Cursed/Dark items seem to last an exceedingly long time, if not indefinitely. Indeed Burgin and Burkes operates by collecting and selling nefarious and ancient items. Further evidence towards this is that Bill Weasley works as a curse-breaker in ancient Egypt, breaking curses from ancient tombs. These cursed items also seem to increase in magical power as they age, or at least the implication in the books is that "ancient curses" seem more potent than more recent ones.


• Some: Potions have the quality of increasing in potency the longer they are left. (The obvious example is the love potion meant for Harry that Ron drank).


• All: Goblin-wrought items seem to have properties that make them near indestructible. In fact there are several examples of indestructible Goblin-Wrought items: the Sword of Gryffindor, and the Goblin-Wrought Helmet that Hagrid gave to the giants. Goblin-made items are also said to "imbibe only that which makes them stronger", meaning that again we have an example of items that with age, will increase in power.


• Special Items:
  
  
  
  • The Sorting Hat seems to be very ancient with the appearance of great wear, but it seems doubtful that it won't last for a very long time still.
  
  
  • The Mirror of Erised again seems to be a very ancient magical device.
  
  
  • The Sorcerer's Stone also presumably would have lasted a long time had it not been destroyed, as it granted "imortality" to the drinker.
  
  
  • Arthur's Ford Anglia, while not a perfect example, does indeed last for quite a while, and one could even argue that the way that it seems to develop a "consciousness" is evidence towards its magical properties increasing.
  
  
  • The Deathly Hallows - These magical items also seem to maintain their spells, until destroyed at least.
  
  
  
  
  

All of the above has simply been evidence towards varying degrees of magical "wear-ness". We've seen items fade over time, but most items seem to maintain their spells until destroyed, or until disenchanted.

We know that the Marauder's Map lasted long (relatively) after all of its creators were dead (as JKR has said in an interview that Harry's son James had nicked it from him and was using it while he attended Hogwarts). We also can suspect that the creators intended for the Marauder's Map to continue to be used by individuals after them. This may not be obvious, but since they require the user to "solemly swear that they are up to no good", and declare when their "mischief" is "managed", it seems likely that they intended that the Map be able to be used by other "mischievous" students.

As such I think it is safe to assume that the Marauder's Map falls into the category of magical items that maintain their magic, presumably indefinitely.