A piece of broken glass was used by Mary Culver to slit her throat in 1762 as part of "one of the most remarkable rituals in history", (PROSE: The Adventuress of Henrietta Street) in which she used the Supplication of the Anakim to allow herself to be possessed by Compassion. (AUDIO: Sabbath Dei)
The piece of glass was permanently stained with her blood. (PROSE: The Adventuress of Henrietta Street) Lord Sandwich kept it in a locked box in the Hellfire Club's headquarters in Medmenham Abbey, where it was stolen by a member of the Service and delivered to the Earl of Bute, who gave it to Sabbath for study. Sabbath used it to perform multiple incisions on his arms. (AUDIO: Sabbath Dei)
The glass was definitely used to summon something. Whenever I draw blood with it, I can feel them. The presences. Trying to communicate. Using my flesh as a medium.
Though Sabbath didn't draw enough blood to fully summon them, (AUDIO: Sabbath Dei) the Great Houses did use him as their agent to arrest Cousin Justine. (AUDIO: In the Year of the Cat)
Two decades later, Scarlette owned the piece of glass, and she wore it on a cord around her neck as a totem. In 1782, Scarlette lent it to Juliette Vierge before her wedding as the "borrowed" part of the "old, new, borrowed, blue" ceremony; unknown to Scarlette, Juliette had already been using it in her bedroom experiments, and she quickly became possessive over the totem. When she left to join Sabbath, she took the glass with her, but she later returned it to Scarlette by way of Rebecca Macardle.
When Scarlette married the Eighth Doctor in 1783, she wore the totem as "something old", a relic of Hellfire Club tradition. Anji Kapoor's TARDIS key, "something borrowed", joined its chain around her neck. (PROSE: The Adventuress of Henrietta Street)