Morgul-knife

But other curses were applied to the blades as well. The Steward Boromir had a shortened life defined by crippling pain after being stabbed by a Ring Wraith. Plus, the blade was designed to break, facilitating the sort of wounds suffered by Frodo. When this happens, the rest of the blade turns to dust, but the shard in the person does not. Which seems like a bit of a flaw. Without that feature, the blade could still be useful, just not as much. Or it could be repaired rather than totally replaced.   It appears to me that the influence of the One Ring might be a factor in why the blade had different impacts on different people. The Steward Boromir did not ever interact with the One Ring. He appears to have never been in any danger of the sort of issues Frodo faced. But the One Ring slowly corrupts the wearer and the Nine Rings also have the same effects of the blade. Which makes me think that the fact that Frodo wore and was still under direct influence of the One Ring allowed for the wraith conversion effects of the blade to manifest.

Given the magical properties of the blades, it makes sense to me that they were made by Sauron. We can assume then that Mt. Doom was essential for this process. We know that he used Mt. Doom for a huge amount of his magical forging, yet the One Ring is the only specific item named as a product of this work. So it appears likely but unconfirmed.

These were the knives used by the Ring Wraiths. But their most notable property is the ability to draw people totally and permanently into the wraith world when a shard reaches a person's heart. Should a person fall prey to this, they become enslaved to Sauron's will the same as if they were corrupted by one of the Rings of Power.   The wound Frodo received required divine intervention, finally totally healed once he reached the Undying Lands. Kingsfoil at least slows the effects of the poison. The difficulty of the healing process though might be in part due to the two weeks between the injury and when Frodo was able to get medical care. Each anniversary of the stabbing on Weathertop it caused serious illness. The wound also hurt badly in the presence of the Witch King.