How to Upgrade a Wood Barrel to Iron
Get the Upgrade Item
The first step in the barrel progression is the Wood to Iron Barrel Upgrade. This is a crafting_shaped recipe. Gather the ingredients shown in the recipe and arrange them in the crafting grid to produce the upgrade item.
Apply It to Your Barrel
Hold the Wood to Iron Barrel Upgrade and use it on your wooden barrel block. The block is converted in place into an Iron Barrel. Because the upgrade is applied directly, the barrel does not need to be broken and its stored items are preserved.
If you do not already have a wooden barrel, note that the Iron Barrel itself can also be crafted directly with its own crafting_shaped recipe. The upgrade path exists so you can convert an existing wooden barrel without losing what is inside it.
Continue the Chain
Once you have an Iron Barrel, the progression continues upward. Craft an Iron to Gold Barrel Upgrade and apply it to reach a Gold Barrel. From there, a Gold to Diamond Barrel Upgrade takes you to a Diamond Barrel. Each step uses the same method: craft the matching upgrade item, then use it on the barrel of the lower tier. Every upgrade is applied in place, so you can climb the entire tier list without ever emptying a barrel.