At the moment, the arc of materials until endgame feels like a bit of a slog. To fix that and to add more variety to the midgame, I propose adding a couple new metals and changing up the material progression for tools and weapons.
The first new metal is copper. It comes after stone in the progression. While not as plentiful as stone, it’s more plentiful than iron. In addition, it’s an ingredient in a number of recipes that remain useful even up until endgame.
The second new metal is bronze. It comes after copper in the progression, and is the first alloy. Making bronze bars in the furnace requires copper ore and tin ore. Bronze is used primarily for tools, weapons, and armor, and doesn’t factor into endgame recipes the same way copper does.
The third new metal is tin. It’s not used directly for tools and is instead a secondary requirement for some recipes, including bronze.
Because of the addition of copper and bronze tools, iron is pushed northward on the progression a bit. Stone tools are used up until roughly level 5, copper tools until level 15, bronze tools until level 25, iron until 35, steel until 45, hardened steel until 55, and then the endgame materials begin.
How do you feel about this?