After Abel cast his first "white bone armor," a new skeleton symbol appeared on the Horadric Cube's skill tree. This meant that the spell was approved by the cube itself. From this point onward, if he wanted to use the "white bone armor" spell, he just had to activate it from his cube.
With another flip of the human-skin book, Abel found a spell rune for a new spell. The name was "clay stone guard," which was what the grey-hooded priest used to guard against spell attacks.
"I'm pretty lucky today, huh."
The "clay stone guard" was a summoning-type spell. That much was clear, but the book didn't talk about how it should be turned into armor. It didn't matter, though. All he had to do was to summon a clay stone guard from the ground.