Copper, Brass and Bronze:

Copper has high thermal conductivity! It heats up quickly and evenly but also reacts readily with acids. So using pure copper cookware to make dishes with tomatoes, tamarind etc are a no-no.

Copper accumulation in the body can lead to copper poisoning over time, which is why copper cookware and its alloys (brass, bronze) are often sold with a coating of tin on the inside. The Tin coating prevents the leaching of Copper. Tin does not react with acids quite as much as Copper does. The body absorbs Tin very poorly. Even on accidental consumption, tin just exits the body in the feces.

So, always buy copper cookware that has been lined with tin. Non-cookware vessels just to hold water, or whisking egg whites, etc are perfectly fine without tin coating. With cookware though, over several years of usage, the Tin coating may wear off...in which case you have to get the vessel re-Tinned.