How do you use engineering prototypes? I'm recieving them but they can't be used

[Enluu-argent-dawn]

So I’m doing Engineering and got myself to level 40. I keep getting these random Prototype items, but I cannot actually use them. They’re just saying cannot be learned and everytime i use them it cancels out. Isn’t this how we get the recipes?

[Tuomas-dragonblight (Tuomas)]

there is 2 types, specific ones, that you can just use to learn(sometimes need to be in combat, or a dead friend or such) then there is the unknown? or such that you can turn into plans with your skill