The Cauldron is a block in Minecraft. It was originally used for Brewing, but this method was not judged to be user-friendly, so the Brewing Stand was introduced instead. However, it remains the only way to get Water into The Nether, which is necessary for an efficient Nether brewery because of the time it takes to enter and exit Nether Portals.
When the Cauldron was first introduced, one would fill it with Water from a Water Bucket. Then they would right-click with the ingredients for the potion. For example, if they wanted to make a Potion of Fire Resistance, they would right-click the full Cauldron with Nether Wart and then Magma Cream. It was then possible to, using a Glass Bottle, scoop out the potion. This was deemed not to be user-friendly by the Mojang team, however.
When right-clicked with dyed Leather Armor, the dye will be washed off.