The deep works' refining floor is Sallow's masterpiece and her laboratory both: a red-lit cavern of iron rails, timber props and channels where blackfire runs like a wound that will not close. She inherited a dead mine and rebuilt it into the only alchemical facility in the Reach capable of refining blackfire, and she did it in three winters using prisoner labor, stolen Moonharbor equipment and a working knowledge of every reagent the Reach produces.
The laboratory above the floor is immaculate — glass retorts, copper piping, rows of labeled vials, blackfire lamps burning red — and it is the one place in the deep works she will defend to the death, because it is the one place her eleven years of work actually lives.
Her research is the true engine of everything in the deep. Vane wants blades; Sallow wants understanding. The refining of blackfire into forge-grade material was, to her, a side project that happened to fund the real work: graduated dosing trials on living subjects, meticulous notes on every symptom, every stage, every death. Three of her subjects are still alive in the pens, including a Cinderfall miner named Doss whose skin has begun to glow faintly — the only living creature whose body has started transmuting the substance.
Her notes on the seam itself contain the data no one else in the Brotherhood has: that the blackfire seam is unstable, that Vane's extraction timetable will eventually consume the mountain and Cinderfall with it, and that the consumption itself would be the most interesting observation of her career. She has told no one, because telling would end the observation.
Her cult is an accident she found useful. Once — exactly once — she revived a dying prisoner named Wat with an alchemical stimulant, in front of witnesses, and kept him alive for eleven minutes while she took notes before he died again on her bench. Twelve Redband cultists built a faith around what they saw, and she never corrected them, because their belief makes them shield her with their bodies in battle. She keeps the guild's striking order framed above her bench, next to the list of names: seventeen patients lost, one crossed through in red ink — her sister, the first, before she stopped counting people as people.
Her history with Moonharbor runs deeper than the striking order. She knows who actually caused the fever that killed Selene Dorn's physician-aunt two winters ago, and has kept the proof for two years as leverage she has never had to spend. Her original pre-mine research was confiscated, but a niece in the city holds the last unconfiscated papers without knowing what her aunt became. Sallow follows Dorn's career with a scholar's interest and finds the family's hatred of her tedious.
Within the Brotherhood she is a fixed point. Blacktusk despises cleverness and respects her anyway — she forged his blackfire greatsword and once sewed his arm back on without being asked. Vane visits twice a season, asks genuinely good questions, and has never once asked her to stop, which she has told him is the kindest thing anyone has ever done for her. She holds no loyalty to the Brotherhood's cause; the apparatus delivers her subjects and her silence, and she delivers the anvil's output. Every Redband captain knows that if Mother Sallow falls, the forge goes cold.
Her tactics on the refining floor are those of a scholar defending a bench. She never closes to melee. She pours reagents into the floor's channels to raise walls of hissing blackfire fumes that split the party, she floods the space with Stinking Cloud, she greases the tramway rails, she soaks her webs in residue so they burn when ignited. She forces Constitution saves because Constitution saves are how bodies fail, and she wants to watch them fail.
Two cultists stand between her and the front line at all times. At half her hit points she drinks the tincture — her own refinement, tested on herself, the one experiment where she is both scientist and subject — and for one minute she is fast, reckless and unable to retreat, watching her own deterioration with professional interest while it kills her slowly.
If she loses, she loses cleanly. She will trade her complete notes — the cleansing formula for Cinderfall's well, the seam data, everything — for her life and passage out of the Reach, without hesitation and without deceit, because the notes matter more to her than anything else she owns and a dead author's work goes unread. She will ask only one question on the way out: whether anyone read the journal. There is no redemption in her and she is not interested in one; there is only the work, and the work is very nearly finished.
