Overall could make some more advanced chains. For example my original thought was:
Apple trees (and other trees) yield an unit of "tree" that does not have [WOOD] tag -> must be taken to custom building "lumber yard" where it is sawed (wood cutting) into 1-3 logs + any other products such as apples (LY_REACTION_MATs).
I didn't implement that due to a lack of time and wanting to preserve overall familiarity to get started. But I think if more advanced production chains are devised we'd all be fine with them implemented retroactively to old materials in new updates.
A more realistic smelting process might have at least some of the following details, based on my poor understanding of metallurgy:
Have one or several "smelting preprocessors" (kilns, but could call them something else and have several different ones) that feed into the vanilla "smelter", with the following details.
* Native minerals (meteoric iron, gold, copper, native silver, native lead, etc) do not require either flux or fuel to make into bars, and do not yield slag. They don't need to be processed further. This is to balance more difficulty in the others.
* For the rest, they must first be processed. This takes x amount of nuggets and yields y amount of separated metal and x-y slag. Realistically you would have to figure out exactly what is needed ore by ore, but for our purposes could generalize to:
- Higher value (harder, higher melting point) metals need more fuel (for a higher temperature, common sense), up to 10 units per unit of ore
- More rare metals yield more slag and less metal, up to 10 nuggets yielding 9 slag and 1 metal (again common sense, reflects how much metal is in the ore)
- Most metals require flux as a purifying agent to smelt. Potash should also work as a flux.
* Processing yields "separated metal" which is technically an ore that can then be vanilla-smelted (melted) into bars. If you want to get realistic you could occasionally call yours an oxide or whatever, but we're not really being that realistic overall.
* There could be alternative metal-dependent processing routes that give less slag and more metal for ore in return for a more difficult setup, such as using various chemicals for leaching. If we had "copper ore" (e.g. bornite), could have "roast copper ore": 10 ore + 10 fuel -> 5 slag and 5 separated copper and "leach copper ore":5 slag + 5 ore + bucket of acid -> 7-8 separated copper.
I think civilizations would still have material access, because the permitted reactions seem to deliver that. (like halfling access to iridium currently despite no access to smelting).
It would take some concentrated effort to make the basics of all the above but after that it would be only slightly more work per metal to add in new stuff than usual. I'm not sure if the above would be total overkill or just more fun though.