Bronze Age

Iron came after bronze, and now it does in Eco too. Vanilla Eco goes from stone tools straight to the Bloomery and iron. Storm Veil Bronze Age puts the age in between back: a new ore, a new metal cast by Miners, a full set of bronze tools, and one small change that makes the Bronze Age matter. Nothing in the game is overridden.

Tin

• Tin Ore is a new ore in Grassland, Wetland and Warm Coast rock, in different biomes from copper, so bronze makes two regions trade, much like the real Bronze Age tin trade. It is mined with any pickaxe (hardness 2, like iron) and crushed and concentrated at the vanilla stations, from the Arrastra and Rocker Box up to the Froth Flotation Cell.
• Copper is about 2.5x as common as vanilla, so bronze doesn't starve copper's other uses.
• Stream tin. Most ancient tin came from river gravels, not mines. Digging sand or clay near water now and then turns up 1-2 Stream Tin pebbles (one block in 20); six of them wash into a Tin Concentrate at the Rocker Box. It works on any world, so even an old world has a slow tin source.

Bronze is cast, not forged

• Miners build a Casting Pit (Masonry Table, Mining 1: 10 Mortared Stone, 20 Clay, 10 Crushed Rock, 10 Wood Board). It is two blocks long, a clay furnace and its sand mold bed, burns wood or charcoal, and needs only a tier 1 room, so adobe is enough.
• Cast Bronze (Mining 1): 3 Copper Concentrate + 1 Tin Concentrate + 2 Clay Mold -> 6 Bronze Bar + 2 Slag. Bronze Bar is a Metal for the Basic Metallurgy research paper and can back a currency.
• Bronze Fittings (Mining 2): 2 Bronze Bar + 1 Clay Mold -> 4.

Seven bronze tools (Casting Pit; pickaxe and shovel at Mining 1, the rest at Mining 2; 8 Bronze Bar + 2 Clay Mold + 6 Wood + 2 Plant Fibers each)

Hammered tin bronze was harder than early bloomery iron; iron won because iron ore is everywhere, not because the metal was better. So the bronze pickaxe, shovel, axe, hammer, hoe, sickle and machete last about 1.4x as long as iron (still short of steel) while iron hits harder (bronze pickaxe 1.5 damage to iron's 2, axe 1.25 to 1.5, shovel 2 blocks a scoop to 3). They are repaired with the Mining skill on Coarse Stone or a Whetstone, the vanilla tool talents apply to them, and any worn bronze tool recasts into 4 Bronze Bar (Recast Bronze Tool, Mining 1), the way Bronze Age hoards were gathered for the crucible.

The iron gate

The Bloomery, the only early iron furnace, now takes 4 Bronze Fittings on top of its vanilla ingredients. That is the only vanilla recipe the mod touches. Everything iron, the Anvil included, sits behind that one gate, and a Smith's setup is vanilla plus a handful of fittings bought from a Miner. No skill level changes anywhere, and room tiers are unchanged.

Worlds

Tin ore only appears in a freshly generated world. On a world generated before the mod was installed, the mod still loads, finds no tin ore, says so in the server log, switches the Bloomery back to its vanilla recipe so iron stays possible, and leaves stream tin and everything else working. Each new world logs one line with how much tin, copper and iron it generated.

Settings (Mods/StormVeilBronzeAge.json, or the Bronze Age tab in the server console)

• BloomeryNeedsBronze (true) and BloomeryBronzeFittings (4): the iron gate.
• TinAbundance (1.0) and CopperAbundance (2.5): ore density, new worlds only.
• StreamTinOneIn (20) and StreamTinWaterRadius (3): how often and how close to water stream tin turns up; 0 turns it off, and the change applies without a restart.

Installation

Extract the zip into your server's Mods/ folder, so the files land in Mods/StormVeilMods/Bronze Age/ beside Mods/StormVeilMods/StormVeilFramework_<version>.dll (bundled; if another Storm Veil mod already gave you the same or a newer framework, keep one copy). Then generate a new world. Players don't install anything: the server sends them the tin and bronze blocks, the Casting Pit and the icons (BronzeAge.unity3d).

Goes well with Storm Veil Prospecting, whose Panning Sluice gains a Pan for Tin job when this mod is installed.

Made by Storm Veil Gaming. Bugs and suggestions welcome in the comments.