A knife with a glass blade, originally owned by Cinderella, that played a hand in the telling of the fairy tale.
The knife has the power to alter a person's body chemistry when they are stabbed with it, able to turn the whole body into glass. To have this effect, it has to stay in the person until they are entirely transmuted into glass. If the knife is pulled out of the victim before they are completely vitrified, they are restored to normal.
The glass knife was used by Cinderella during the events that inspired The Brothers Grimm original tale; this story, however, was re-edited by the Warehouse to keep the artifact a secret. In the story Cinderella had a pair of glass slippers, but the real Cinderella had a knife that turned people into glass.
This artifact first appeared in the modern era in 1961, when two young women who were secretaries for a magazine publishing company were found dead, and it seemed that their bodies had been turned to glass. It was assumed that the girls' boss, Jonah Raitt, killed them, and that he got away with the artifact after killing his wife and yet another secretary. The case was reopened in 2010 by Rebecca St. Clair; Pete and Myka used H.G. Wells' Time Machine to go back to 1961 as Jack and Rebecca to change the future. While in the past, they discovered the murderer wasn't Jonah, but rather his wife, who believed he was having affairs with the other women. Pete and Myka buried the artifact under a cherry tree in an orchard; in the present (2010) they dug it up and it's currently in the Warehouse.
- The handle of the knife is decorated with etchings of the astrological sign Capricorn and the sea-goat it represents.
- The constellation is said to be ruled by the planet Saturn, the Roman name of the Titan Kronos, frequently conflated with the embodiment of time, Chronus.
- In Greek mythology, the goat Amalthea (with which the constellation is sometimes said to be based on) suckled the infant Zeus after he had been hidden from his father Kronos to avoid being eaten.
- The constellation is also dubiously connected to a likely modern story of the sea-goat Pricus, who was created by Kronos and shared his ability to manipulate time. He had many children, all sea-goats, who would travel to land and instantly lose their tails and their ability to speak and think. To prevent this, he turned back time again and again, but eventually resigned himself to loneliness. Learning he cannot change their fate and not wanting to be the only sea-goat, he asks Kronos to kill him, but as he cannot die he is instead placed among the stars as the constellation Capricornus.