Here is an old example of using some sort of "chisel" tool whacked by a hammer, to incise lines in a metal figurine.
https://www.metmuseum.org/art/collection/search/309944
Dram the lines and follow them by tap-tap-tap-tapping the chisel tool onto the metal shaped body / tank / thingamajig.
The metal body needs to be annealed along the lines and then re-marked.
Pitch can be used to fill the inside, hardened up, and then it becomes the "anvil" against which the metal is driven -TAP-Tap-Thunk-thunk-whack-whack-bappitty-bap.
The hammered lines are then dressed with a fine file, and then sanded with 320 grit, and is then buffed out, for polished work.
Y'all should just give it a few blisters' worth of your time, Sandmanred. Dividends of deep understanding would then be your prize.