I came across some photos earlier today that are relevant to this project. This project involves using as few raw materials as possible, and using raw materials that are as simple as possible. How exactly the simplicity of a raw material should be defined is a difficult question to answer: simple with respect to what? A context must be given.
In the south west of England there are a wide range of natural resources available. There are locations in the southwest where ores of copper, tin, lead and iron can be found within a few dozen miles of each other. A few years ago I found some tin ore (cassiterite) and had a go at smelting it.
I didn't keep a detailed record at the time of how I went about this. The account below is to the best of my recollection.
I dug a hole about one foot in diameter, one foot deep, and conical in shape (but smooth rather than pointed at the bottom). I lined it with clay (the clay occurred naturally a few feet down in the location where I made the furnace). About one third of the way down one side I made an air inlet. I lit a wood fire in the hole to harden the clay. Once this fire had subsided I cleared out the ashes and made another larger wood fire in the furnace. I piled on a lot of wood, overflowing the top of the furnace. Once the wood on the top of the furnace had burned down, and glowing embers were left, I sprinkled coarsely crushed ore into the centre of the furnace and then raked up embers to cover it. I blew into the air inlet to raise the temperature of the furnace. I did this for perhaps 15 to 30 minutes. Once the fire had cooled (I think it had been burning for between 1 and 2 hours in total), I used a trowel to carefully remove the ashes from the fire and spread them out on a clean sheet of plastic. I recall that there were still some small charred and unburned twigs right at the bottom of the cone. Amongst the ashes I found a few small globules of tin.
A second attempt the following day wasn't so successful, but did still result in a few small balls of tin.