Made from brass "door kickplate". Full size mock-up was done in posterboard, then cut out and transferred to brass with a big nail. (scratched) To cut the pieces out I carefully drilled many small holes all the way around the outline of each piece, (!) 'till I could break the pieces off by hand, (that's a lot of holes. to drill.) then cleaned each piece up better on a grinding wheel (don't do this! dangerous). After that I used a hand grinder and small files to finish right up to my lines. I then attached the pieces to the helm with rivets. I used the big nail to scratch some subtle decorative borders.
I made this B.I.. (Before Internet), so those little bits of information will be more than I had to start with. My friend wanted something in brass on this helmet, eyebrows, cheeks, and such. I had an idea and a piece of metal. For more information than I could even, search Armour making.
If you can dream it, you can make it! Just be extremely careful when working with nifty high RPM tools.