Creating a rainbow or iridescent patina on metal surfaces is a popular technique in art, jewelry, and DIY projects. This stunning effect mimics the natural oxidation process while adding vibrant, shifting colors. Here are the most common methods to achieve this eye-catching finish:

1. Heat Coloring: By carefully heating metal with a torch, you can create a spectrum of colors due to thin oxide layers forming at different temperatures. This works well on stainless steel, titanium, and copper.

2. Chemical Patinas: Specialized patina solutions, such as those containing ferric nitrate or liver of sulfur, react with metals like copper or brass to produce iridescent hues. Layering these chemicals can enhance the rainbow effect.

3. Anodizing: Primarily used on aluminum or titanium, anodizing involves submerging the metal in an electrolyte bath and applying an electric current. The resulting oxide layer refracts light, creating a shimmering finish.

4. Oil Slick Technique: Applying a thin layer of oil to heated metal can produce a rainbow sheen as the oil burns off, leaving behind colorful residue.

5. Vapor Deposition: A more advanced method, this involves coating metal with thin layers of metallic oxides in a vacuum chamber, resulting in a durable iridescent surface.

Each technique offers unique results, so experimenting with different metals and processes can help achieve the perfect rainbow patina for your project.