Referring to the originals as "brass" is a modern hobbyism/collectorism.
Brass is an alloy of copper and zinc. Bronze (in the 19th century aka "gun metal" is/was an alloy of copper and tin (sometimes with trace other metals like nickel or zinc).
It was somewhat common for the Confederates to smelt down bronze church bells for their firearms industry. Depending on the mix, more copper in the alloy would make it redder and one sometimes sees it in their revolver frames as well as uniform buttons.
Brass, especially when alloyed with added lead for easy of casting, makes an okay BP gun frame for plinking and even for m moderate shooting. IMHO, there are far more people pouring rounds of repro's than likely ever did originals.
There is tons of literature and on-line comments on "brass frame revolvers' and their flaws of shooting out of alignment, etc. But, in brief, with the lack of power in BP loads even filling the chambers, warping a frame requires a lot of shootings. However, a common problem is that high use "chews" up the arbor mount in the recoil shield and worse yet the back of the steel cylinder pounds it way into the recoil shield area due to repeated recoil.
Originals did not suffer from that because they were made of gun metal (bronze) which is harder than soft brass, and were not NUG fire thousands of times.
But, most people, even educated and experienced firearms people and authors, usually always call them "brass" whether CS revolvers, Henry, or Winchester rifles.
Yeah, I can't 'get' people to stop referring to the Remington Model 1863 "New Army" Revolver as a M1858 Remington either.