• Popokkuli tells you that Ansobert has escaped from his warehouse. Travel to the Sapphire Avenue Exchange, and there search for the merchant's lady attendant.
• Ansobert's distressed attendant reveals that there is a strange rumor surrounding her master. Travel to Erralig's Burial Chamber and speak with her once more.
• The distressed attendant confesses to you that the remains found outside the city walls were those of her friend who had gone missing. To continue the hunt for Ansobert, travel to Revenant's Toll and speak with Popokkuli.
• Ansobert confesses to the crime of murdering the woman whose corpse was found outside the city. You have seized Heartstrike, and all that remains now is to use it to free Niellefresne from the blade's curse. Return to the Alchemists' Guild to speak with Severian.
• Severian informs you that the curse on Niellefresne can only be broken by destroying Heartstrike and leaving not a trace of it behind. Use a set of dissolvent ingredients to mix a vial of potent dissolvent , and then deliver it to Greinfarr at Erralig's Burial Chamber.
• You have seen the vial of potent dissolvent to Greinfarr's hands. Freed at last from the curse of Heartstrike, the remains of Niellefresne and the young lady glow the color of aether before disappearing entirely. Speak once more to Greinfarr.
• Greinfarr has spoken his peace. Return to the Alchemists' Guild and relay to Severian the deep gratitude of F'lhaminn and her friends.
• Before returning to his alchemical duties, Severian leaves you with the wisdom that learning to live with the loss of loved ones forces us to face our own weaknesses, and that it is an inevitable part of life itself. His trust and confidence in you have grown by the resolution of this affair at your hands. No doubt your adventures together are far from over.

Potent Dissolvent can be found under Logs -> Crafting Log -> Special Recipes -> Class Quests