Short story where a travelling psychic dispels a toxic aura from manufactured goods [duplicate]

Question

I'm not sure where or when I read this. Probably 1980s or 1990s, but it might have been a magazine or an anthology.

The story is set on a post-technological (fallen) world where technological advancement is blocked by an unexplained invisible aura that might be called "shadow." The aura, which makes people sick, will grow on anything made, but the more artificial it is, the faster the aura grows and the stronger it becomes. If I'm recalling the back story properly, a colony starship landed, but before they could accomplish anything the entire ship was enveloped, and the colonists had to flee with essentially the clothes on their back. Generations later, there is a society existing at approximately mediaeval level; they haven't lost all knowledge, but can't use anything more advanced than simple hand-worked metal tools.

The protagonist is one of a special guild who fight these auras. Because he is specially sensitive, he sees the auras as a dark haze around objects, and can easily identify them and tell how strong they are. He travels from town to town, destroying the auras on people's tools so they can keep using them. He does this by a psychic effort, fighting the aura into submission; it is very draining and he can only do so much in a day. I remember a mention of how fighting the aura means taking some of the darkness into yourself, which affects his mental state and maybe his health.

In one town he becomes alarmed when he finds they have far too much metal for one of his guild to keep the auras under control. He is introduced to someone who claims to have a new way to fight them, which I recall as "mindlight." Instead of dominating the dark aura, this person creates a brightness that drives it away. When this is demonstrated, the protagonist is temporarily blinded; his connection to the aura has made him sensitive to the brightness too.

I'm not sure where the story went after that; I recall one more scene but it may have been from a sequel.

In this scene an enemy has managed to create a large number of swords and is threatening to conquer a town. The swords are stored in a tent in barrels so the people who drive away the auras can keep them clear, and the protagonist's side sneaks in and dumps a huge amount of powdered metal all over everything. Because of mindlight they can manufacture it, but the other side with the traditional way of dealing with auras is overwhelmed. (The resulting aura was bigger than the tent and visibly expanding as they snuck away.)

Answer 1

I'm going to post my own answer since the linked question doesn't cover many of the points in my question. The exact story I'm thinking of is "Not Always to the Strong" (1986) by Timothy Zahn.

The back story is, as the above comment notes, mostly from "The Shadows of Evening" (1983) and is covered in this answer. The bit about the ship that brought the original colonists to Vesper is from this story:

The old colony ship that had brought mankind to Vesper hadn't been approached since the day it landed, the day when its seven hundred passengers and crew ran gasping from it and the Shadow which had begun to grow around it. For a while they'd feared the Shadow might grow forever, engulfing the whole planet in agony, but it had finally stopped. Legend had it that right by the ship itself the Shadow was dense enough to kill.

And in the present:

An hour before noon, he reached Lander's Waste.

The term "waste" was somewhat misleading, since it looked no different than the area immediately surrounding it. Native Vesperian plants and animals thrived there, completely unaffected by the eight-mile diameter Shadow that had enveloped them for the past two hundred years. A ring of red granite boulders, laboriously moved there by the original colonists, marked the Shadow's edge. Just for practice, Turek used his afterimage technique and confirmed the edge was still where it always had been. No surprises there. Someday, he knew, the ship at the center would start to fall apart, its tools and machines collapsing back into dust-and when that finally happened, the Shadow would begin to shrink.

The specific scene I recall is the climax of the longer second story "Not Always to the Strong" in which an ambitious young kinglet named Krain from the town of Masard has taken advantage of advances in metallurgy resulting from the Mindlight effect to forge swords with which he plans to go a-conquering. Krain recruits Turek to join them for their first conquest, the town of Lazuli where the school of the Mindlight masters is established.

Krain nodded, the pleased look back on his face. "We have a group of smiths right in Masard turning out ten blades a day."

"With your new Shadow Warriors standing by to keep Shadows away from the final product," Turek nodded. "But you can't be making the metal itself, because to get an alloy strong enough for a sword blade you'd have to start with almost pure copper and tin. Three Shadow Warriors couldn't even begin to keep up with the Shadows that would grow-never mind the advanced smelters you'd also have to have." He gestured toward the hidden sword. "Someone in Lazuli developed this alloy, didn't they? Someone with a Mindlight Master or two standing over his shoulder. What did you do, sneak into the village and steal some of the metal?"

"More or less." If Krain felt any guilt over his action he hid it well. "But don't worry about that-we have enough to make all the swords we'll need to bring Javan to his knees. And after that we'll have both the smelter and the Mindlight Masters and can make all the weapons we'll ever need." The northman leaned back in his seat. "But I think you've heard enough to make your decision. What say you, Master Turek?"

Turek joins up, but doesn't really want to see Krain succeed, so he comes up with a plan to stop his army. Turek steals some copper dust from the foundry in Lazuli:

The copper dust was astonishing, and more than a little frightening. Barely five minutes after scooping it out of the bin the effects of the Shadow growing around it were becoming painful; within ten Turek was forced to stop and clear the Shadow away. Never before in his life had he seen a Shadow grow so quickly, and for a long moment he wondered if he would ever be able to get the dust back to Krain's encampment. But he really had no other choice. Gritting his teeth, he picked up the bucket and kept moving.

And uses it to sabotage the swords:

Inside was unrelieved darkness; but Turek needed no light for what he was going to do. Dropping the waterskin by his foot, he raised the basket chest-high and, with a single convulsive movement, flung its contents over the neatly stacked swords.

The result is a massive shadow that makes the sword unusable:

Krain broke the silence. "The Shadow around my swords is fifteen feet across and still growing," he said softly, the venom in his voice all the more intense because of that. "What did you do?"

Both stories appear, sequentially, in Zahn's collection Cascade Point (1986), which is where I read them, and why I wasn't sure if it was one story or two.