This mold was unfortunately unsuccessful, but I did learn a thing or two about metal. Ten minutes' bike from the farm is a forge and metal workshop, and one of the techniques they use is sand casting. A full-scale pattern is packed into sand, then removed, and molten aluminum is poured into the void.
The pattern and the cast.
I made my pattern quite thin, thinking that metal would allow for an economy of material that wood does not permit. However, when the blacksmith examined my pattern, he remarked that the cast would be liable to break, because cast aluminum is very different from sheet aluminum and can be brittle. He said that it would be better if I brought a solid block with the hole cut out- exactly like First Mold!
The blacksmith examines my pattern.
The cast did not turn out because it was hard to remove from the sand. The sand must be damp in order to hold its shape, so the pattern must be 'smooth like glass'.