"Don't get too excited, none of the duplicates are actually worth anything."
-- Miranda Goshawk (BoS)
When touched, the target object will multiply, but the copies are worthless and will tarnish or break down over time. The spell needs to be stopped by the original caster, or the objects will continue to multiply for hours or days.
Also known as the “Gemino Curse” (BoS).
History and Notes
The spell was discovered by Helixa and Syna Hyslop, who were twin witches. They used the spell on literally everything they owned, leading to a duplicate of everything existing inside their mansion (BoS).
References from the canon
- Gringotts placed Gemino Curses on the objects in the Lestranges' high security vault, creating a lot of apparently identical copies from which the genuine objects could not be distinguished. According to Griphook, a would-be thief who continued to handle treasure under such a curse would eventually be crushed by the weight of expanding gold (DH26).
- Hermione uses this to duplicate (in appearance, anyway) the locket Horcrux so that Umbridge won't realize that it is missing (DH13).
from "geminare" L. to double (Gemini is the constellation known as "The Twins")