The Rod
Volta's lightning rod needs an onyx bar. Five onyx ore from Cloudreach, smelted, brought here.
“Onyx. Five ore from the rocks in Cloudreach, smelted to a bar. Bring it here and I'll build a rod that outlives us.”
Onyx rocks are in Cloudreach's south-west. Mining 50, and the furnace is back in the Yard.
EastScape Wikibuilt from the game itself
onyx ore
onyx bar