"First things first, don't try to enchant an already forged weapon, because the chances of it failing are very high." Blake nodded in approval.
"The reason is that every material possesses a certain resistance to mana and as you all know an array deals with mana. This amount of resistance a material has to mana is dependent on the nature of the material.
Wood has the highest resistance because it isn't a mana conductor, while the mythical metal called, kranus is said to be the best mana conductor. As for the rest, you can go read them up. Professor Mack didn't care about the snarls some of the students made, nor did he have any plans of punishing them.
"As for the best opportunity to engrave an array on, let's say a sword. That would be immediately after the sword has been hammered to its desire and you have to make sure it is still red hot.