Use the Crystal of Deep Shadows near the Altar of Shadows to deepen your attunement to the altar, then return to Andrion Darkspinner in Shattrath's Lower City.
- WARNING!* You can only select one tailoring specialization.
Deepen Altar of Shadows Attunement
Crystal of Deep Shadows (Provided)
If you become a shadoweave specialist, you will make twice as much shadowcloth as an average tailor and have access to several exclusive patterns.
Of course, any tailor can use the Altar of Shadows, but a shadoweave tailor possesses a deeper attunement to the altar, unlocking powers that few can fathom.
Take this crystal to eastern Shadowmoon Valley, and find Netherwing Pass leading south from the Netherwing Fields. Near the world's edge, you will find the Altar of Shadows. Use the crystal there.
You will learn: Shadoweave Tailoring
Upon completion of this quest you will gain:
9800 xp or 58 50 at level 70.
+150 Lower City faction
I can see that your visit to the altar was a success. There is a subtle difference about you that few will see, but there's no doubt it's there.