Smelting

Smelting is a method of producing refined goods. It has the same idea as crafting: a player supplies acceptable ingredients, and receives a corresponding output. However, smelting utilizes furnaces, blast furnaces, or smokers, which have a unique interface: one input field for the object to be heated, a secondary input field for the fuel, and one output field for the final smelted product.

For example, two saplings (fuel) could be used to smelt one wood (input) into one charcoal (output). Raw food items can also be cooked using a campfire (without giving experience), while smokers and blast furnaces can smelt certain types of items twice as fast as usual at the cost of giving half as much experience and being completely unable to smelt any other items.

Usage and mechanics
To smelt with a furnace, an input material and a fuel must be placed into the top-left and bottom-left slots of it, respectively. The furnace begins to smelt on its own and continues to work if the menu is closed and the player leaves. The player can tell whether a furnace is working or not by seeing if the furnace is lit and the fire particle effects are appearing or not. When the furnace begins to smelt, it consumes one piece of fuel and the fire gauge fills. Once a piece of fuel begins burning, it cannot be stopped, unless the furnace is broken. While the piece of fuel burns, the fire gauge slowly decreases until it is gone, and the process repeats with the next piece of fuel. When all fuel is exhausted with material remaining in the input slot, the furnace stops, and the item is not smelted. If the input material is exhausted with fuel remaining, the fire gauge continues decreasing, wasting the remaining burn time left for the piece of fuel being burned, but no further fuel is burned if the input slot remains empty.

As items smelt, an arrow icon represents the smelting progress. Each smelting operation takes 10 seconds. When it completes, the smelted item is added into the output field. If the furnace runs out of fuel before the arrow is filled up, then the input is not smelted and the process rewinds at double speed.

If the player travels far enough to unload the chunk containing a smelting furnace, the smelting process pauses until the player returns. Smelting also pauses if a player leaves the dimension in which the furnace is located. If the player sleeps in a bed while a furnace is smelting items, the furnace's progress remains the same as if the bed had not been used and no additional time had passed. This is because when a player sleeps in a bed, no time actually passes; the game simply sets the time of day to morning.

If a player removes a smelted item from the output field, that player instantly receives experience for all the items smelted in that furnace, even items that had already been pulled out by a hopper.

Items can similarly be smelted in a blast furnace or smoker. The usage and interface for smelting with both blocks is the same as those of a normal furnace; however, blast furnaces can be used only to smelt ores and metal tools, and smokers can be used only to smelt food items. In addition, both blocks smelt items twice as fast as furnaces do, but only give half as much experience points as a normal smelt. Some items (such as logs) can be smelted only in a basic furnace.

Using a campfire
Items can also be smelted using a campfire. To do so, the player must a lit campfire, with any of the food items listed in the Recipes section in their hand. Fuel is not required; the campfire is able to cook items infinitely on its own. Smelting an item takes 30 seconds, three times the amount of time it would take if a furnace were used instead. A campfire can hold up to four items at the same time. Once the campfire has finished cooking an item, it emerges from the campfire as an item entity. No experience points are granted.

Gem ores
The following ores can be smelted, but in these cases this is unnecessary and wasteful. All of these ores yield their product freely when mined with an appropriate pickaxe and give far more experience than when smelted. The ore blocks themselves can be obtained only via the Silk Touch enchantment. Also, some of these ores may drop multiple items when mined normally, and all of them potentially drop even more when mined with a Fortune-enchanted pickaxe. Smelting these, however, always gives only a single unit of the product.

Tools, weapons, and armor
A note about fractional experience values: For fractional values, first multiply this value by the number of smelted items removed from the furnace, then award the player the whole-number part, and if there is a fractional part remaining, this represents the chance of an additional experience point.
 * For example, when smelting 1 coal ore and removing the coal, the value is 0.1, so this grants a 10% chance of getting 1 experience point.
 * Or, when smelting 5 sea pickles and removing all 5 lime dye, the value is 0.2 × 5 = 1, so this grants only 1 point.

Fuel
There are multiple fuels that can be used to smelt items. The type of fuel that should be used depends on the number of items in question.

For larger jobs, a single lava bucket or a block of coal can burn more items than can fit in the furnace—both input and output are limited to a stack of 64, but a block of coal burns 80 items, and lava can burn 100 items.

Hopper automation
The smelting process can be automated with hoppers on the top and bottom of the furnace. For larger smelting jobs, a third hopper can feed in fuel and, in case of lava being used as fuel, any empty buckets come out of the bottom hopper. This automatically feeds and empties the furnace so that different materials can be smelted in the same batch with no loss.

Any experience from items smelted is saved even if the furnace is completely emptied by a hopper. If one cooked/smelted product item is later taken out of the furnace, the player receives experience for any items that were smelted.

Video
Note: this video is outdated, as it doesn't talk about blast furnaces, smokers or campfires, because this video was recorded before 1.14.

Trivia

 * It takes 10 minutes and 40 seconds to smelt a stack of 64 items in a single furnace, although this time can be reduced by splitting the load between multiple furnaces or by smelting the items in a blast furnace or smoker.
 * Burning logs or wood with planks to make charcoal is over 4 times (×4.57) more efficient than using the log or wood itself as fuel. It is just over 1$1/4$ times more efficient than using planks.
 * The most efficient fuel to make charcoal is charcoal itself.
 * Turning coal into blocks of coal is slightly more efficient (×1.11) than using the coal itself as fuel. For 9 coal, you get 80 smelts instead of the usual 72.
 * If the player wants to use wooden tools as fuel, the most efficient way is to use it until its durability reaches 1, then use it as a fuel afterwards.
 * Melting down used iron – or golden – tools and armor for nuggets and crafting the same tool out of them afterwards is a more efficient strategy in the case of shovels, swords and hoes (the latter two just barely). Otherwise, the player can get far more durability for their iron by combining the items in the crafting grid or a grindstone.
 * "Smelting" is a pretty broad term in the context of Minecraft while in the real world, smelting has a more precise definition.