Diamond Tables are decorative pieces of furniture that can be crafted in your Crafting Menu (opened by "Q" as the default key) or at Crafting Tables (that still exist on older worlds), but only after the crafting-recipe for Diamond Tables has been unlocked by taking/crafting an Iron Table for the first time (which in turn is unlocked by taking/crafting an Obsidian Table). To craft 1 Diamond Table, you'll need (as of R29 in March 2016): Crafting/taking a Diamond Table for the first time will unlock the crafting-recipe for Lumite Tables.