The Fourneau Bread Oven is made from cast iron, and is "seasoned" after being made to protect it from oxidation. This seasoning is nothing more than a thin layer of vegetable oil that is baked on at high heat so that it polymerizes; this baked-on oil prevents rust and is also what gives cast iron its black color.
Cast iron cookware of any kind requires some basic care:
1.) Keep it clean. After baking, brush out any crumbs and flour left behind.
2.) Never soak the Fourneau in water. Wash it without soap and dry it immediately by hand. Don't let it "air dry."
3.) After washing, rub it with a light coating of oil.
4.) Occasionally, you will want to build up the seasoning. This involves rubbing it with a light coating of oil and baking it in your oven at around 485 for 30-60 min.
The Fourneau is a bit different than a skillet in one way that will affect how you'll want to care for it ...
Bear in mind that the Fourneau really almost never needs to be washed! If you primarily use it for baking bread, there is really nothing to "clean." All you need to do is brush out the crumbs and flour as stated above.
Our recommended best practice is to give the seasoning a "tune-up" every couple of months. (See step 4 above). If you store the Fourneau in your oven, you may need to do this more often, especially if you bake a lot. If any rust spots develop on the Fourneau, they are easily removed with steel wool or a stiff wire brush. Simply brush off the rust, and continue with seasoning as described above.
Observing these basics should help keep your Fourneau looking as beautiful as the day that you received it for a long, long, long time. (Like a forever long time ...)
For even more information about cast iron, check out this great article on Serious Eats!