"...Plutonic Bronze quite naturally occurs as an alloy of arsenic, tin, and, of course, copper.
"It's smithying has long been noted a deathly and morbid pursuit. Laming even the strongest of smiths as legend reports. The superiority of such blades even to quite excellent, tin heavy bronze is unquestionable.
"These are arsenical bronze only, however. True Plutonic Bronze is quite rare. It may only be mined by the blind and those condemned to die. Deep, deep, deep are the rare shafts in which the veins lie. The casts must be lined in the wizard's own blood and poured in the black of a moonless night.
"According to Meilanachus, wounds caused by Plutonic Bronze blades cannot be healed. To be frank, Your Grace, I've never investigated a claim by Meilanachus that was not true. I urge you to handle the blade as little as possible. Were you to nick your thumb, the cut shall stay with you unto your grave, may God-most-Censorious keep that day long at bay..."
- Excerpted from private correspondences of the Beige Duke..
It's all true, except the blood on molds thing. Which means you don't actually need a wizard, but, like, no wizard is telling anybody that.
Wizardry is a real feast or famine sort of business. The biggest customers always are rich assholes who want other rich assholes dead.
Anyway what it says on the tin. Damage done by these blades does not heal. So a PC getting popped for 8 damage from a Plutonic Bronze spear when they're level 2, 12 HP, they're gonna be at 4 HP tops, going forward. (until leveling or whatever)
If you have magical healing in your games, that don't work either. Sans the direct intervention of a powerful god, the wounds DO NOT heal.
Cuts that aren't held closed in some way, will of course continue to be a problem...
The Baron's Pie Knife
Unadorned Plutonic Bronze Cinquedea, 1d6 Damage.
+1 to hit, +2 Damage against folx in less than Chain Armor. Damage dealt by this weapon cannot be healed.