This begins in Gunthak. Look for Grennik Neltrin, a female human behind the bank area, in a building near a brew barrel.
You say, 'Hail, Grennik Neltrin'
Grennik Neltrin says 'Hello. Have you been exploring the island? I came here to discover the secrets of the Broken Skull trolls but I have yet to even explore the island. Rumors that their high priest Nadox held the power to cure any disease have been drifting around Norrath for some time. I've come to see if the rumors are true. Unfortunately the island is much more dangerous than I had imagined and I haven't found anything useful. If you find anything having to do with the troll High Priest, please bring it to me.'
Head to the fort area in Gunthak with the outcasts. Druids can forage the Gunthak Gulf Water in this area. The rest have to kill the Plunderers at the fort. Any one of them (troll, DE, erudite) can drop the water.
Next, head to Crypt of Nadox. Head into the north section, opposite the Luggald area, and hunt Furious and Vehement Blackhands. They are light to dark blue to level 60s. Broken Skull Clan Blood is a semi-common drop. In the same area are Broken Skull Initiates and Adherents, which drop the Blackened Vials. They are also semi-common.
Return to the bridge over lava and head to the Luggald area. Pure Blood drops from Luggald Abominations and Initiates and is super rare, and these things are tough. Dark blue to level 61 and around 10,000 HP. Plus, the room respawns pretty quick.
Once you have all the pieces, head back to Gunthak. There's a brew barrel in
the back area. This used to require brewing skill, but enough people bitched at
SOE and they made it no-fail.
Combine a Blackened Vial, Broken Skull Clan Blood and Gunthak Gulf Water in a brew barrel to make a Black Potion.
Combine the Black Potion with some Pure Blood (again in a brew barrel) to make a Glowing Black Potion.
Hand the Glowing Black Potion to Grennik for the Pure Blood scroll, which is Nodrop.
This spell is a must-have. It will cure multiple poisons and diseases, including slows. A player can have 3-4 poisons and diseases on them and it will wipe them all out in one cast. Keep it memmed for raids.