There is really supposed to have been a prince from Wertheim who was murdered with a glass sword like this one here. He was called Prince Dominik Marquard Sebastian Christian of Löwenstein-Wertheim-Rochefort.
In 1735 this prince is supposed to have stayed in Venice. At the time trade had not been a lucrative business for a long time and sections of the Venetian aristocracy were poverty stricken. But not our prince from Wertheim. He threw noisy parties and surrounded himself with beautiful ladies. It was only a matter of time before people began to begrudge him his frivolous lifestyle, and murder was a popular medium used to eliminate disagreeable opponents at the time!
But our prince must have been protected by magic, because several murder attempts were made before he was killed. The first assassin ambushed the prince in the dark with a dagger, but this rebounded off him as if he were wearing chain mail. And the bullets from the pistol used in the second murder attempt didn’t seem to touch him because he escaped uninjured, even poison seemed to have no effect whatsoever.
It was only when his servant betrayed his secret to the Venetians that he was killed. The Prince was supposed to have learnt incredible skills from a Spessart poacher that rendered him immune to poison and metal. The Venetians immediately had the glassmakers in Murano make a glass dagger and this is what became Prince Dominik Marquard Sebastian Christian of Löwenstein-Wertheim-Rochefort’s end!