The Thaumium Helmet is crafted like any piece of vanilla armor, on a Worktable; only you have to use Thaumium Ingots to do so.
Thaumium has a higher durability than iron (275 vs. 165 for the Helmet), and is also easier to enchant.
By combining this with the Goggles of Revealing in an Arcane Worktable, you can craft the Helmet of Revealing.
Crafting recipe[]
The Crafting Recipe
Place 5 Thaumium Ingots on your Worktable: 3 on the first row, and one on each side of the middle row.