Tobho Mott was a smith from Qohor who knew the spells to rework the metal.
Tobho had learned to work Valyrian steel at the forges of Qohor as a boy. Only a man who knew the spells could take old weapons and forge them anew.
A Game of Thrones - Eddard VI
Ice was reforged by Mott. (at least it was in the books)
"Nor I, my lord," said the armorer. "I confess, these colors were not what I intended, and I do not know that I could duplicate them. Your lord father had asked for the crimson of your House, and it was that color I set out to infuse into the metal. But Valyrian steel is stubborn. These old swords remember, it is said, and they do not change easily. I worked half a hundred spells and brightened the red time and time again, but always the color would darken, as if the blade was drinking the sun from it. And some folds would not take the red at all, as you can see. If my lords of Lannister are displeased, I will of course try again, as many times as you should require, but—"
A Storm of Swords - Tyrion IV
"You have done good work, Master Mott," Lord Tywin told the armorer. "My steward will see to your payment. And remember, rubies for the scabbards."
A Storm of Swords - Tyrion IV
The secrets seem to be available only to Qohorik smiths.
The properties of Valyrian steel are well-known, and are the result of both folding iron many times to balance and remove impurities, and the use of spells—or at least arts we do not know—to give unnatural strength to the resulting steel. Those arts are now lost, though the smiths of Qohor claim to still know magics for reworking Valyrian steel without losing its strength or unsurpassed ability to hold an edge.
The World of Ice and Fire - Ancient History: Valyria’s Children
Only here, in all the world, has the art of reworking Valyrian steel been preserved, its secrets jealously guarded.
The World of Ice and Fire - The Free Cities: Qohor
