Thank you for the opportunity to answer this question. Every year at Christmas Time, we here in NJ have a re-enactment of Washington Crossing the Delaware. We show up in period costume.
At Washington's Crossing, the village and Inn where Washington stayed, along with the boat house, boats, and accessories, has been completely restored.
The really interesting thing is, we fire up the fireplaces, and haul out those "COPPER" Apple Butter kettles, in order to have some tasty, hot spiced apple cider, made just like the old days.
Yes, your kettle is copper. Brass is not malleable enough to form the kettles. The brass appearance would come from one of two things. Copper can be alloyed with materials to make it have a less oxidative surface, much better for cooking.
AND years of high heat in contact with high carbon environments of those olden day fireplaces could have hardened the surface. The constant heating and cooling action would change the original charter of the copper.
TRIVIA TIME: The ancient Peruvians were able to make copper in an allow that is shinier and more durable than steel.