GregTech 6/Smelting

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In GregTech 6, only a few metals can be smelted in a vanilla Furnace (Copper, Tin, Zinc, Lead, Bismuth). For other metals and alloys, the new Crucible system must be used.

Burning Box

Main article: Burning Box

Crucibles are heated from below by a Burning Box.

  • An air block must be in front of the Burning Box.
  • Heat comes out the top based on the heating rate in HU/t, different for each Burning Box.
  • The fuel's burn rate is determined by fuel efficiency and heating rate.
  • Most types of spent fuel leave behind byproducts such as Dark Ash.
  • Any flammable objects within 3 blocks can be ignited.


The heat content of fuel is determined by multiplying the number of vanilla smelting operations by 5,000. The most common fuels are shown below.

Fuel Heat Content (HU) Byproduct Burn Time* (s)
Lignite 10,000 Tiny Pile of Dark Ashes 15.6
Coal 40,000 Small Pile of Dark Ashes 62.5
Charcoal 40,000 Small Pile of Ashes 62.5
Coal Coke 80,000 Small Pile of Dark Ashes 125

(* Burn times are shown for Lead/Bronze Burning Box)

In a Burning Box, 1 Coal Coke is equivalent to 2 Coal, in the case that Railcraft is not being used. Lignite is useful for generating a small amount of heat so the Crucible does not accidentally melt down.


Main article: Crucible (GregTech 6)

Crucibles are placed on top of Burning Boxes and hold the smelting materials.

  • The material is placed into a Crucible in the same manner as a Cauldron.
  • It is able to store up to 16 ingots/dust or 144 nuggets/tiny piles worth of material.
  • Any additional material thrown into a full Crucible will be lost.
  • Rated by mass (kg) and maximum temperature in Kelvin (K).
  • The max temperature is equivalent to 1.25x the melting point of the material used to make the Crucible.
    • Exceeding max temperature will destroy the Crucible and anything inside.
  • If the material thrown in has a liquid type that is labeled "Acid! Handle with Care!", the Crucible will be destroyed unless the Crucible is acid-proof (e.g. Chromium).
  • While being heated by a Burning Box, 1 HU will raise the temperature of 100 kg of mass by 1 K.
  • Mass includes the contents and the Crucible itself, rounded up to the nearest 100 kg.
  • If the Crucible is not being heated, its temperature will decrease at a constant rate (biome dependent) due to heat loss to the environment, regardless of the mass. For example, in a Forest the Crucible and contents will lose about 2 K/s until it reaches the normal Forest temperature of 289 K.


Main article: Mold (GregTech 6)

Molds can be created from the same materials as Crucibles, and give shape to molten materials.

  • Molds are placed next to any of four Crucible sides.
  • Right-clicking on a mold causes it to be filled with valid molten materials inside the Crucible.
  • Shape is determined by chiseling pieces out of the mold. For example, the Plate Mold has all 25 pieces chiseled out. Other valid mold shapes can be found in the Smelting Crucible Manual.
  • Any invalid shapes will produce nuggets equivalent to the number of chiseled pieces.
  • Freshly poured items will be very hot and must be allowed to cool before grabbing them, otherwise damage will be taken.
  • Temperature drop in a mold is about 100 K/s.
  • Molds have maximum temperatures just like Crucibles (1.25x the melting point of the material used to make it).


To smelt an alloy, the Crucible must reach a temperature above the melting point of the alloy itself, and all but one of the components. For example, when smelting Iron from Yellow Limonite and Dark Ashes, the melting point of Iron (1811 K) is sufficient because it is greater than or equal to the melting point of Yellow Limonite (all but one of the components). Properties of alloys can be found in Book of Alloys.

Temperature Management

Proper management of temperature is crucial to the Crucible smelting system. Exact temperatures cannot be determined until Thermometer Sensors are built, which require Steel. However, recipes can be followed "blind", or new recipes can be created with some math. Fuel use can be planned out for a given smelting operation if the properties of smelting materials are known. Melting point, boiling point, and mass of material components can be shown with enhanced tooltips (F3 + H). For example, the tooltip for Crushed Copper Ore will show two components, Copper (1.222 units) and Stone (1.0 units), along with melting point, boiling point, and mass for each.

The rate of temperature increase is inversely proportional to the amount of mass stored in the Crucible; the more material thrown into a Crucible, the slower it will heat up; conversely, the less material there is the faster it will heat up. Some alloys (such as Iron) have a smaller mass than the sum of their parts, so the contents will begin to heat more quickly upon reaching the temperature at which the alloy is formed. The Heat rate of a given Burning Box is constant, but temperature change depends on the mass.

The Crucible is most in danger of melting down at the end of an operation when all the materials have been poured out and fuel is still burning. Some materials can be used as moderators to limit the risk of destroying the Crucible. A Gold Ingot has very high mass and high boiling point, so it will often absorb enough heat to protect the Crucible. If there is any Copper in the Crucible, Lead can be used instead, otherwise the Gold and Copper could alloy to form Rose Gold.

Recipe: 4 Bronze Plates

This is a common first step in smelting in order to produce the Bronze Plates needed to craft a Bronze Burning Box.


  • Lead Burning Box: 50% efficient, 16 HU/t
  • Ceramic Crucible: 2500 K max, 688 kg
  • 1 Ceramic Molds (chiseled out)
  • 3 Copper Ingot (or 27 Copper Nugget)
  • 1 Tin Ingot (or 9 Tin Nugget)
  • 3 Coal or 6 Lignite

Important temperatures for this operation:

  • Forest environment: 289 K
  • Melting point of Tin: 505 K
  • Melting point of Copper: 1357 K
  • Melting point of Bronze: 1357 K


  1. Throw all Copper and Tin into the Crucible. Total mass is now 4500 kg when rounded up, Crucible included.
  2. Place all fuel in the Burning Box.
  3. Light with Flint and Tinder.
  4. Inside the Crucible, Tin will melt first.
  5. When the contents turn into a Bronze-colored liquid.
  6. Pour into the plate mold by right clicking on it, wait 15 seconds in average, then grab the cooled Bronze plate (x4).
  7. At this point the Crucible should be completely empty.
  8. When the fire goes out you can extract the Tiny Piles of Dark Ashes in the burning box.
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