According to Vetron's Guide to Weapons and Armour, the glass sword has an effectiveness rating of 127, compared with 90 for a cannon. While the Black Sword can also kill in a single strike, Vetron lists its power as "unknown."
Glass swords first appeared in Ultima V, in the same location of the Serpent's Spine where the White Stone was found in Ultima IV. When the appropriate tile is searched, the game checks the player's inventory and reveals a glass sword if there is not one in inventory. In this way a party of six could possess up to seven at a time, by readying six party members with them (which removes them from the general inventory).
In Ultima VI, glass swords could be found as loot, or could be made by a glassmaker in Minoc, who demanded peer gems and money for his work. A glass sword was needed to make the Britannian Codex lens.
In VII/2, the Avatar was given a glass sword before setting out to Serpent Isle, but it was lost almost instantly upon arrival in a Teleport Storm; it was eventually found by Hazard the Trapper. Glass swords were also sold by Pothos of Moonshade, for 1500 Guilders each.
Glass swords could also be found in Ultima IX, but they were weaker -- some enemies could survive a single strike.
It is known that blades of purest crystal may be found in the mountains of the Serpent's Spone. Such was the magic in their forging that they will not fail to strike any foe, and no mortal being will survive their wrath. Then will the Sword shatter into a thousand harmless shards, never to fight for its wielder again.
A historical legacy of death. These single-use swords will almost always kill any creature in a single blow, but they are seldom useful for a second opponent.
Unfortunate is he who is struck with a glass sword, for contained within is a powerful magic that enters the body and mangles the innards. In the release, the sword is destroyed and cannot be repaired. Thus, a glass sword is a rare and fortunate find. Should you find one, save it for a foe who inspires a novel fear.
- In Ultima VI, glass swords were useful for destroying doors as well as killing monsters, though sometimes more than one had to be used.