One thing is certain, a forno is a handmade object.
Since the oven wasn't going to build itself, I went to work. By foot, in big rubber boots, I mixed clay with sharp builders sand, then I packed it by hand over the wet sand dome Nathan and I had sculpted, to create the 4-inch-thick cupola that forms the oven body. This is the oven's thermal mass. Along with the fire brick floor, it will collects and hold the heat from the fire and radiate it back into the cooking food.
After it had dried for two days, I scooped all the sand out from under the hardening dome. To speed things up a bit, I lit a drying fire. If I'd wanted, I could have cooked pizza, but since the oven will work better with another coat of insulating clay, and will look better and last longer with a final coat of finishing plaster, I'll get things a little more finished before I throw that dinner party.