On the morning of Day 2, Quill was gone. His bed was covered in an endless, luminous pink jelly that smelled of laundry soap and vanished when it dripped onto the floor (S5).
Master Vul drew all of it into a corked ceramic flask. He says the flask doesn’t trap anything and is “meant to keep this shape safe”; whatever is inside can leave by itself.
Tested by Kale: it is excellent soap. It flows back into the flask afterwards, and it removes all the hair it touches.
Is it Quill? Nobody knows.