Part of History

Probably a waste of a post, but as of this moment this seems entirely unobtainable if you didnt earn it during Legion.
I used a level boost before BFA came out and did Legion content, and was not awarded this at all.
I even did the Mage order hall story during BFA, hitting 110 and 120, and was never awarded this.
As an ATT collector it's really sad to forever not have 100% in the Order Halls because two appearances are locked behind Artifact Knowledge and Artifact Traits and Power from weapons.

This achievement is reward for hitting AK25 and unlocks a new artifact color tint.

Important: You cannot unlock this tint for your artifact weapon until after you have unlocked the entire tier. In other words: you must complete the Class Order Hall Campaign before this tint will unlock! I found this out the hard way and had to submit a ticket when I got the achieve, but did NOT get the new unlocked appearance! The above information is the Blizz answer to my dilemma.