Crystal Singing is a method of shaping elven crystal, a substance given to the elves by the goddess Seren. The shaping can be undone with the Ritual of Reversion. After completing the quest The Eyes of Glouphrie, players are able to sing crystal into weapons, armour and tools by using the Singing bowl in the Ithell Clan district in Prifddinas.
By "singing" with certain frequencies, the elves are able to shape the crystal into practically anything. They use this to create a variety of equipment, as well as structures; their capital city, Prifddinas, was shaped in this way. The process of singing is still somewhat mysterious, and no human is ever known to have done so on a high level comparable to that of elves' singing.
Based on bits and pieces of information gathered in various quests, the process of crystal singing apparently involves emitting sounds of frequencies beyond the human auditory range; the crystal responds to those sounds by morphing into various useful shapes.
Crystal Singing can also be performed using bowls that have been shaped in such a way that their curves create a sound similar to the "Singing" normally performed by elves. Such a singing bowl in the Ithell district in Prifddinas can be used to sing Crystal tools, weapons and armour. Other singing bowls exist, but have limited uses. One can be used to sing crystal chimes in Yewnock's cave and another can be used to sing crystal saws in Brimstail's cave.
The use of enchanted flutes in crystal singing is supposedly attested in an unavailable part of the logs of the explorer Samuel Scourduel, which is in turn referenced by archmage Perien in The Harmony of the Runes.
In the quest Within the Light, the player character seems to begin learning the basics of crystal singing, as they enchant two crystals to teleport to the Temple of Light. The Prisoner of Glouphrie also indicates that other races than elves, such as humans and gnomes, also possess to an unknown degree the gifts necessary for crystal singing. However, it is unclear as to how much a human or gnome could further their gifts.