The case and delightful strap with security chain tests for 9ct gold but it’s not hallmarked, so it’s probably Gold plated. The winding crown also has the logo and the strap has very little wear with a good working clasp.

Additional Material: Gold Or Gold Plated
Original/Repro: Original
Product: Watch
Style/Period: Art Deco
Age: Post-1940
Maker: Omega