Grathmeld (グラスメルク, gurasumeruku?, lit. "Glassmerk") is a system that was developed by Shurelia after she banned the direct use of Sound Science to the humans in which Grathnodes can grant their power to the items as "Granted Magic", and they are basically minerals containing supernatural powers. Depending on the differences between their special characteristics, the crystals have one of these four colors: Red, Blue, Green and Purple, and these are the groups in which they are divided.
To explain more in-depth, Grathmeld is the process in which the characteristic wave frequencies (Spectrums) of the Grathnode Crystals are scanned by the Silver Horn, and then, it runs a program depending on that frequency, granting the Symphonic Power and effects carried in the crystal to the item. The people of the Wings of Horus developed this technique even further, to the extent of even being able to make airships with it. The people that practice this technique are known as Grathmelders, or by the shortened form, Melder. This technique was spread at the start of the Third Era by a man and a woman called Gasaki and Leila. Who they were, from where they came, and what happened to them is still a mystery.
Grathmeld has so many applications and uses that anyone that masters it will be able to make any kind of item, ranging from the simplest medicine and healing potions, to high-class food, powerful weapons and armors, weird accessories, and even airships. Needless to say, this technique is unique to the region of Sol Ciel because the Silver Horn's area only covers the broadcast range of the First Tower of Ar tonelico, and because it was developed after Mir's Rebellion, long after the Towers had become isolated from each other, there was no way in which it could be spread to the other regions at the time Ar tonelico: Melody of Elemia takes place.
The most recognized Grathmelder in the current times is Professor Pochoma, who lives in Karulu Village with his granddaughter, Noelle, and gladly teaches Grathmelding to anyone who wishes to learn about it.