As most of you know, in 4e D&D there is a material called residuum, essentially the same as the various arcane dusts that enchanters create by disenchanting magic items in World of Warcraft. A variant form of residuum shows up in the Vox Machina campaign (Exandra shows a lot of 4e influence), but otherwise it’s not a part of D&D 5e as far as I know.
In 4e, characters can use the Disenchant Magic Item ritual to convert it into residuum equal to 20% of its gold piece value. You can then use residuum as a universal magical component for rituals (remember, all rituals cost some amount of money in 4e), and Enchant Magic Item is one of those rituals. Also, if you sell a magic item, the rules say that you get 20% of its gold piece value. The result is that residuum is identical to and measured in gold, so it loses any sense of being an independent object.
In 5e, magic items are much fewer in number by default, there’s no disenchanting mechanic, the enchanting mechanic takes enormous amounts of downtime for very rare or higher items, and selling magic items is meant to be inconvenient and time-consuming as well (as we see in XGTE).
I actually don’t care much at all about being able to roll up a bunch of residuum into new magic items. I’d rather see it become a way to turbo-charge the enchanting process – expend an ounce of residuum, do a week of work in a day, maybe?
I want to put some hurdles around the buying and selling of residuum, because pure fungibility with money bugs me so much.
My top priority is creating the dramatic moment where you’re out of diamond dust or another key component that you can’t do without, and in your desperation, you disenchant magic items to pay the cost. This applies to revivify, raise dead, resurrection, and true resurrection most of all, of course – sacrificing to restore the dead to life is about as pure of a fantasy moment as I think you could want.
Disenchant Magic Item
3rd-level abjuration (ritual)
Casting Time: 1 minute/special
Components: V, S, M (a porcelain mortar and pestle)
You choose one common or uncommon magic item, which you must touch throughout the casting of this spell. When you finish casting the spell, the magic item is turned into residuum dust. You gain one ounce of residuum dust for every 50 gold pieces of the magic item’s value. You can’t disenchant a magic item that is attuned to another creature, and a cursed magic item can’t be disenchanted. A magic item conjured or created by a spell of limited duration is destroyed, but doesn’t create residuum.
If you are attuned to the item, the casting time of the spell becomes 1 action.
At Higher Levels. When you cast this spell using a spell slot of 4th level or higher, you can target a rare magic item; using a spell slot of 6th level or higher, a very rare magic item; and using a spell slot of 8th level or higher, a legendary magic item. This spell can’t affect artifacts.
Design Note: I’m well aware of how weird it is to talk about a ritual that uses an 8th-level slot. That’s Not A Thing in official 5e. I don’t think this presents a problem, though – if you have unrestricted access to unattuned magic items and 11 minutes at a time to spend, I honestly don’t care how many of them you dust. Don’t try to trap a PC with this spell inside a magical object unless that object also denies spellcasting or all actions – but dimension door is the central reason for that, not disenchant magic item. If you’re in the bad guy’s armory with unrestricted access, uh, that was a bad mistake on their part.
Wondrous item, common
This purplish dust has a curious silvery gleam. One ounce of residuum can replace 25 gold pieces of expensive material components used to cast a spell. If the residuum was created within the past 24 hours, one ounce can replace 50 gold pieces of expensive material components used to cast a spell. Residuum is always consumed when it is used as a material component, even if the spell doesn’t usually consume its components.
When you are creating a new magic item, you can expend 1 ounce of residuum as part of a day of work. If you do, you complete a week of work instead. You can’t use residuum to replace the material costs of crafting a new magic item.
Let’s Go Shopping
What does this do to residuum in the market? Ideally, it muddies the waters of its gold value-per-ounce a fair bit. No one assumes you can get fresh residuum unless they have a special deal worked out, so it’s probably not going for more than 25 gp per ounce.
As compared to using the Selling a Magic Item downtime action, you’re dodging the 25 gp up-front cost, the investment of time, and the chance of complications, and in return you’re defaulting to the lowest magic item offer (50% of base price).
To the right buyer, of course, greatly increasing the speed of magic item creation could b wroth a lot, and a universal expensive spell component is phenomenally valuable. Maybe you do carry two and a half pounds of residuum with you just in case you need to cast heroes’ feast, because Sly Flourish won’t let you have your 1000-gp chalice. You – or someone – had to dust 2000 gp of magic items to accomplish that – four uncommons or one rare.
The upshot of this? The price probably gravitates toward 25 gp per ounce, but can go a fair bit higher or lower. Let’s casually call it as low as 15 gp, or as high as 50.
It’d be pretty cool to get maybe 1d3 ounces of residuum, some of the time, when you destroy a construct or some kinds of elementals, and especially when you destroy a living spell in Eberron. (Eberron would have a highly developed residuum economy and supply chain, possibly monopolized by House Cannith.)
And… I think that about covers it for residuum.