Coal bag

The Coal bag is a reward purchasable from the rewards trader for 4,000 Dungeoneering tokens. It requires a Mining and Dungeoneering level of 35, however at least level 40 is required to earn the tokens needed for the coal bag, unless you win them through other means such as Sinkholes or Treasure Hunter. Only one coal bag may be in the player's possession at any time.

The coal bag holds up to 81 pieces of coal. When smelting or superheating, coal in the bag will be used before the coal in the inventory. It is refillable just like the rune essence pouch, though it does not degrade.

This item cannot be traded or dropped but it can be destroyed. The bag must be empty to be destroyed; otherwise, the player receives a notification regarding the coal still left inside the bag. Mined coal is not automatically stored into the bag. Instead, players must manually use a coal on the bag. When coal in the player's inventory is used on it, all pieces of coal (up to the limit) are deposited into the bag. You may also primary click on the coal bag and select the fill option, filling it with all coal in your inventory.

Upon player death, the coal bag is completely lost along with any coal inside if it is not kept as one of the three items. This item will not appear under your gravestone.

A fill option to deposit all the coal in your inventory is available while having the bank opened with your coal bag in your inventory.

Uses
This bag provides an additional 81 coal slots and is useful for both mining and smithing as it allows players to increase coal ores carried per trip. It doubles the amount of bars per inventory you can have.

The first column identifies the type of bar to be made. The second indicates how many pieces of coal should be in each bag. The third represents how many of the primary ore (Iron, Mithril, Adamant, Runite) is required. The fourth column represents how many free inventory slots remain. The fifth column shows how many bars are produced. The last column indicates the experience received from smelting a full load (including coal in the coal bag) of that ore.

Blast Furnace (starting with an empty inventory)

Other Furnaces or using a Explorer's ring 4 (starting with an empty inventory)

Superheat Ores (start with nature runes and a fire staff equipped)

Trivia

 * Regardless of the amount of coal in the bag, it weighs 0 (even though 81 pieces of coal = 183).
 * The coal bag used to cost 20,000 Dungeoneering Tokens before the 21 April 2010 update.
 * Mod Chris L stated on the "Live Q&A New Skill - Answers" that the coal bag originally only meant to hold 10 coal "but when I went ingame to test it myself after making it, I realized it was a bit rubbish! I ended upon 27 as it meant you could smelt more runite ore per inventory, it worked out nicely".
 * Smithing elemental bars takes the same amount of coal and yields the same number of bars as mithril, but only at the furnace of the Elemental Workshop, as no other furnace is hot enough to smelt the elemental ore.
 * While bank booths offer the ability to empty the coal bag whilst using the banking interface, bank deposit boxes do not. This means that you must exit, empty, and re-enter the bank deposit interface to unload the coal from your coal bag. Or alternatively, use a piece of coal on the box, select "4: All", empty some coal out of the bag, and repeat.
 * Unlike most interactions, attempting to use a random item on the coal bag will not yield the "Nothing interesting happens." dialogue.
 * The amount of coal held by the coal bag was increased, from 27 to 81, on 20 July 2015.

Coal bag Coal bag