"The Queen of Air and Darkness" by Valerie Holt Pendragon

This is Morgause, queen of Lothian (Ireland), sister of Morgan le Fay, and half-sister of King Arthur as she is portrayed in T. H. White's The Once and Future King. Though not as magical as her sister, she dabbles in sorcery when it suits her fancy, such as when she boiled a cat alive to find the bone that made one invisible. Here, she tries her hand again.

The Queen opened the coffer in the darkness and stood near the moonlit patch from the window, holding a strip of something in her hands. It was like a tape.

The strip was a less cruel piece of magic than the black cat had been, but more gruesome. It was called the Spancel - after the rope with which domestic animals were hobbled - and there were several of them in the secret coffers of the Old Ones. They were a piseog rather than a great magic. Morgause had got it from the body of a soldier which had been brought home by her husband, for burial in the Out Isles.

It was a tape of human skin, cut from the silhouette of the dead man. That is to say, the cut had been begun at the right shoulder, and the knife - going carefully in a double slit so as to make a tape - had gone down the outside of the right arm, round the outer edge of each finger as if along the seams of a glove, and up on the inside of the arm to the armpit. Then it had gone down the dife of the body. down the leg and up it to the crutch, and so on until it had completed the circuit of the corpse's outline, at the shoulder from which it had started. It made a long ribbon.

The way to use a Spancel was this. You had to find the man you loved while he was asleep. Then you had to throw it over his head without waking him, and tie it in a bow. If he woke while you were doing this, he would be dead within the year. If he did not wake until the operation was over, he would be bound to fall in love with you.

Queem Morgause stood in the moonlight, drawing the spancel through her fingers.