cleaning brass with what?

[Matt Lukes]

Yeah, any weak acid will do- vinegar is acetic acid, citrus fruits have citric acid, uric acid would do although it's a rather less desirable choice LOL And it only needs be a dilute solution, so not much would be requred- regular table vinegar is 5% acetic acid by volume, and you can cut that in half by diluting with water and it still works just fine. Given the abundance of wine in the ancient world, I'd guess vinegar would be the most commonly-used 'pickle' for copper alloys.