The metal was nickel silver 8% and is 1mm thick. The B/ham UK supplier wouldnt let anyone into their w/shops to see how they did it. Their Commercial advantage a kept secret.
The other way is hydraulic forming. The "T" shaped "Yorkshire" copper plumbing fittings are made this way from a length of strait tube.
Metal will flow cold if you use enough energy,
To mention an example of this, yesterday, i had a local s/smith badger me to see my w/shops and I happened to have in the drop stamp a flat hammer and a brooch die some 2 us quarters side by side in size. I put 1, 1.5mm thick blank on the die with a identical shape in 3mm 999 ali on top to act as a force.
the hammer weighs 275 lbs and I dropped it some 18in. The ali came off twice the size and too hot to hold
just from the one strike and the copper blank( for enamelling) filled the die just fine. This was also warm.
There was a small flash on the copper, this was put back in the blanking die to clip off. 1880's tech!.
From initial blanking to clipping, 100 an hour.