Opening his palms, Lin Mu quickly let the feather get cooled down, letting its new color set in.
"It's not shiny anymore?" Ashy titled her head in sadness.
"It'll fit better in your feathers and won't catch attention." Lin Mu replied. "Plus it's easier to add the formations now." He added.
The latter was the major reason for doing this, as raw Lustrous Edge Obsidian had a crystal structure that didn't allow for runes to be added properly. It was certainly possible to add them but the number of formations that could be added would be limited to small ones.
But once heated, the crystalline structure changed to another arrangement, which allowed for runes to be added without any clash. This did come with the disadvantage that the durability of the obsidian was reduced, but that didn't matter in the long term once formations for toughness were added.