Separate pieces with edges folded back as flanges and probably riveted since there is no evidence of heat patina anywhere. It might have been tacked with a tig, or soldered. VERY CAREFULLY.
You can see the separate instances of oil canning by the bent corners on the smooth pieces, and there are some small hammer marks from adjusting the edge bend to accommodate the applied bead in several places.

Nice piece.

Gene Olson
Sculptor
Elk River, MN

Pretty close Gene---dimensions are 1300 by 600 on plywood back then plywood shapes 20mm all round smaller than finished metal screwed onto the plywood back--turn metal down 5mm all round on each piece then glued them onto the plywood---I sealed all joints so its waterproof---Thanks for your comment---I am discovering how much there is to learn here------Dick

Hi Rick,
Appreciate your comment---it is made from copper---brass and stainless steel sheet which I bought from local scrapyards----don't know how the colours arrived --maybe it has to do with the quality of the copper?? I'm sure somebody out there can give a better answer----I enjoyed doing this first piece-Dick

Appreciate your comment Frank----must admit I have no idea how or why the colours arrived --yet!!--------Dick

Hey Mystro------your comments have blew me away----I'm getting back into it----thanks---dick

great to have such encouragement dong wan most apreciated---dick

Hya Bob----its 51 inches by 24inches--appreciate comments----thanks ----dick

Thanks Laura-----feel like trying a bit more now