Melted Wax is a crafting ingredient often used for Decors and Furnitures recipes, it can be found in Treasure Chests now and then, but can also be obtained from Keepas of most kinds.
Melted Wax is obtained by melting Beeswax in the Forge by using any fuels.
Its current "melting" time is 10 seconds for x8 Melted Waxes if you use Wood or Leaves for Fuel. Generally the time that the forge needs for each process depends on the power of the fuel you are using.
Melted Wax cannot be put into the quickbar, cannot be placed into the world, and cannot be displayed on Wall Shelves, in Wood Planters nor Flower Pots currently (as of R26 in December 2015).
Melted Wax is not needed to craft any tool, machine, weapon, armor nor lighting. Its main purpose is to be used as a crafting component for Stone Chests, Arctek Chests, Weapon Racks, Stone Wall Shelves, Bedrock Doors, Stone furniture, Obsidian furniture, Iron furniture and many various building blocks.