Alchemy Furnace (alchemy_furnace)

An alchemy_furnace is a furnace specification, not the block in the world. It says how many main and auxiliary slots the furnace has, how many ingredients one batch may hold, how much heat it loses per tick once it is above the set point or the heat stops, and the temperature ceiling of that specification itself (optional). quality is optional: every specification shares the same block item mxt:alchemy_furnace, so the item itself cannot say which tier it is — only the specification the stack carries can: a furnace built to this specification starts on that tier. An mxt:quality component on the stack wins; with no quality here this layer answers nothing and resolution continues to the default_quality registry.

The furnace core carries a specification through the mxt:alchemy_furnace component. Without that component, or when the definition it points at is not in the registry, the furnace cannot be started, and it is never quietly replaced by a built-in specification; placing, saving and breaking the core all keep the component.

File Location

Furnace files go in data/<namespace>/mxt/alchemy_furnace/ within your data pack.

Purpose: Furnace specifications.

The filename corresponds to its ID. For example, data/example/mxt/alchemy_furnace/clay_kiln.json has the ID example:clay_kiln.

Fields

Field	Type	Default	Description
quality	Quality id	none	Optional. The tier a furnace built to this specification starts on.
main_slots	Integer	required	Main ingredient slots, 1..2.
auxiliary_slots	Integer	0	Auxiliary ingredient slots, 0..2.
capacity	Integer	required	Ingredient count per batch, 1..320; the item's own stack limit still applies.
cooling_per_tick	Double	required	How much heat is lost per tick while the furnace sits above the set point or has no heat block, a finite positive number that never crosses the set point: with a heat block in the cell the temperature is pushed towards the set point, and when that cell is empty or holds a block with no heat it falls all the way to 0.
max_temperature	Double	none	Optional. The ceiling this specification itself allows, finite and greater than 0; writing 0 or a negative number is refused at load. Left out, this layer sets no ceiling and the walls and the heat block are the only two left.

The catalyst is fixed to the third slot of the auxiliary store and is not a field. The physical inventories are fixed too: two main slots, three auxiliary slots (two auxiliary plus one catalyst) and four output slots; the main or auxiliary slots a specification does not use cannot be filled. Starting a batch consumes every item in each occupied slot of both input stores, not one item per slot.

{
  "main_slots": 2,
  "auxiliary_slots": 2,
  "quality": "example:common",
  "capacity": 64,
  "cooling_per_tick": 0.5,
  "max_temperature": 120
}

Whenever this specification declares max_temperature, the furnace core's item tooltip prints it as a "Specification ceiling" line next to the slot count and capacity.

The quality a specification writes is the furnace's tier, and it reaches display and use conditions; changing only the quality component on the item changes none of the specification's parameters either. A formula may require a tier of the core (furnace_quality) or of every material put in (input_quality). A better furnace is faster: on top of the recipe's duration, a batch is divided by the core tier's own alchemy_modifier (multiplied with the lowest tier on the material side), so giving a high furnace tier alchemy_modifier: 2 is all it takes — no formula written at all. The core tier's position on its own ladder reaches the recipe's own formula fields only, as the variable furnace_rank; the potency formulas and any alchemy_modifier formula cannot read it. The tier itself does not enter the ceiling — this specification's own max_temperature does: the ceiling is the lowest of three, namely this specification's max_temperature (left out means it does not take part), the lowest rating among the wall materials built into the furnace, and the highest temperature the heat block gives, see the next section. Walls and the multiblock structure never look at quality.

Furnace Structure

A furnace is not a single block: players build a fixed 3×3×3 by hand, with no datapack structure schema and no custom shape.

Position	Block	Role
Middle cell of the front layer	Furnace core	Holds the batch and carries the furnace specification; the heat readout and Set / Start / Abort sit on its page.
Left cell behind the core	Main ingredient input	Two main ingredient slots.
Right cell behind the core	Auxiliary ingredient input	Two auxiliary slots plus one catalyst slot.
Above the middle centre cell (the centre of the top layer)	Alchemy output	Four output slots, extraction only.
The other 18 cells	Furnace casing	Each carries one wall material and opens no screen.

Facing defaults to north, and a horizontal rotation turns the whole shell together; 22 cells are checked in all (the four bottom corners plus the two layers above). Only the four corners count as structure in the bottom layer, and the other five cells are not checked at all: whatever sits there, or nothing, and whether their chunk is loaded makes no difference to forming, and they are never claimed; the corner blocks each draw a quarter of the base, so those five cells can stay empty and it still reads as complete. The centre cell of that bottom layer is the heat cell: what a player puts there is up to them, and only a heat block supplies heat, see heat_source. An incomplete shell, a missing or invalid wall material, or a cell claimed by another furnace all stop it from forming and from starting; the screen spells out in words what is missing.

Temperature Ceiling

The set point a player may enter is capped by the lowest of three:

1. the max_temperature this furnace specification writes. Left out, this one takes no part.
2. the lowest rating among the 18 casings (the max_temperature of the wall material).
3. the highest temperature the heat block gives (the max_temperature of mxt:heat_source; a block that implements the heat interface answers for itself).

With walls rated 200, a heat block giving 150 and this specification writing 60, the ceiling is 60; write 400 there instead and the ceiling is still 150. So a high furnace tier only raises the ceiling by writing a large max_temperature on that specification, and never past what the walls and the heat block give; the other way round, a low-tier specification can hold its own ceiling far down even when the walls take 200.

The set point must be finite and lie between 0 and that ceiling, it may be changed while running, and an invalid request is rejected (the player cannot click the temperature bar past it); the first batch also requires it to fall inside the recipe's temperature tolerance. With the walls or the heat block missing (the ceiling reads 0) the furnace cannot run at all, and a set temperature is refused outright.

The heat block stands in the centre cell of the bottom layer (local index 4, directly below the centre of the furnace above). The mod ships no default heat block and no bundled values for lava or fire.