A Storm of Swords
Lord Tywin Lannister has the armorer Tobho Mott melt down Eddard Stark's Valyrian steel greatsword Ice, to make a sword for House Lannister. Mott has enough metal to make two swords, one longsword and a slightly smaller sword. He attempts to tint the swords crimson for the color of House Lannister, but the metal absorbs the color, resulting in ripples of nearly-black grey and red almost as dark as the grey.
Tywin gives one of the swords to Joffrey before his wedding, replacing Hearteater. Accepting the name Widow's Wail when it is shouted by a guest, Joffrey uses the blade to destroy Lives of Four Kings, a gift from Tyrion Lannister.
Most Valyrian steel was a grey so dark it looked almost black, as was true here as well. But blended into the folds was a red so deep as the grey. The two colors lapped over one another without ever touching, each ripple distinct, like waves of night and blood upon some steely shore.—Tyrion Lannister's thoughts
—Joffrey I Baratheon to his guests