Artefact Compression is a powerful spell used by some mages. The spell encloses the victim in a jade shell and shrinks the victim so small, that they could fit in the palm of their hand. This allows the caster to take the victim prisoner without worry of an escape attempt, as well as hiding the prisoner themselves. Such trauma is very dangerous to the victim and could cause organ damage to them. Should the target survive the compression process, they remain in a stasis and are unaware of their surroundings. When decompressed, victims normally are disoriented, and in a weakened state.
The spell was used on Yennefer by Francesca Findabair after the events of the Thanedd coup, allowing the Queen of the Valley of Flowers to smuggle her colleague off the island and back to Dol Blathanna. She kept Yennefer in the form of a jade figurine for forty-seven days before releasing her and putting her forth as her chosen candidate for the Lodge of Sorceresses.
Artefact compression is also one of the spells used in the PnP RPG game "The Witcher: Game of Imagination".
In the final installment of the trilogy the artefact compression appears in two secondary quests:
We learn that Lytta Neyd compressed them a long time ago and they can only be decompressed by Triss.