Gemino Curse

"Hermione screamed in pain, and Harry turned his wand on her in time to see a jeweled goblet tumbling from her grip. But as it fell, it split, became a shower of goblets, so that a second later, with a great clatter, the floor was covered in identical cups rolling in every direction, the original impossible to discern amongst them."

- Description of the Gemino curse used in conjunction with the Flagrante curse in the Lestrange Vault in Harry Potter and the Deathly Hallows

The Gemino Curse or Doubling Charm (Geminio) is a spell used to duplicate an object, creating an exact replica of the target entity. It can also be used to bewitch an object into multiplying repeatedly when touched, though how one would produce the latter effect is unknown.

History
The Doubling Charm was invented by a pair of reclusive twin witches, Helixa and Syna Hyslop, who used it to create duplicates of every item inside the mansion, in which they lived together their whole lives. After their deaths, their relatives finally learned of this practice, discovering two, duplicated sets of hand-written instructions for the spell, one left by each twin.

Effects
There was much debate over whether a copy created with the Gemino Curse held the same value as the original, as the two items were impossible to tell apart at first, being identical to one another. However, over time, the copy tended to rot or tarnish more quickly than the original, making it possible to identify eventually. Because of this, the replicas created through this charm are considered to have no value or worth. It is also unknown as to whether or not the Gemino Curse can duplicate living or sentient beings, or if it is able to replicate an object's magical properties.

An odd characteristic of the spell, for which a solution was never found, was that only the original caster could stop the multiplication of the object. If for some reason the caster was interrupted in his/her casting, the object would continue multiplying for hours or even days, stopping only when the copies began to break down. As such, it can be presumed that the Doubling Charm may produce both a single copy, or multiple, depending on the caster's intentions. This indefinite replication property could apparently be harnessed as a security measure, with this spell causing valuable objects to begin multiplying out of control when touched by an intruder or potential thief, thus quickly filling up the space with worthless copies of the original object, and trapping or crushing the trespassers.

History of Usage

 * This spell was used by Hermione Granger in 1997, creating an exact duplicate of the locket they had stolen from Dolores Umbridge, and giving the replica to the Inquisitor, so that she would not suspect that the locket was missing from her person. Although the spell created an object with exactly the same appearance, it did not duplicate the the portion of Tom Riddle's soul that was contained within the locket.


 * Employees at Gringotts Wizarding Bank cast this curse as well as the Flagrante Curse on all of the valuable objects within the Lestrange Vault. When Harry Potter, Ron Weasley and Hermione Granger entered the vault in order to retrieve Helga Hufflepuff's Cup, the treasures multiplied repeatedly, and nearly crushed the trio after it had grown so large in number, having formed piles that nearly touched the ceiling. The objects proliferated rapidly, the duplicates multiplying themselves, and duplicates resulting from those duplications, ad infinitum.

Etymology
Latin geminare meaning "to double".

Appearances

 * Harry Potter and the Deathly Hallows
 * Harry Potter and the Deathly Hallows: Part 2
 * Harry Potter and the Deathly Hallows: Part 2 (video game)
 * LEGO Harry Potter: Years 5-7
 * Wonderbook: Book of Spells