WW2 Tombac Luftwaffe Flak Badge by G.Gremer. You can see this information on page 112 and 113 of the book "The Flak Badges"(ISBN: 978-0-9797969-4-4).
Regardless of the material was able to produce a quality product. Zinc, thoug a lower-quality metal than Tombak, took details very well. The eagle´s beak on this example was blunted by some impact, but the rest of the badge is in great shape. Brehmer plated many badges but also used a low-quality Brennlack silver wash on their zinc badges. Here, the silver wash is being absorbed in wavy bands. The low-quality wash was applied with brushes and then heat-dried . The banding may be the original brush marks.