Creating a matte black or gunmetal patina on metal surfaces is a popular technique for achieving a sleek, industrial, or vintage aesthetic. Here are the most common methods to achieve this effect:

1. Chemical Oxidation (Black Oxide Finish):

This involves treating the metal with a chemical solution, such as ferric chloride or liver of sulfur, to induce controlled oxidation. The result is a durable matte black or dark gray finish.

2. Heat Patina (Torch or Flame Treatment):

Applying controlled heat with a torch can create a gunmetal or smoky black patina, especially on copper, brass, or steel. The color varies based on temperature and exposure time.

3. Vinegar and Salt Solution:

A DIY-friendly method involves soaking the metal in a mixture of vinegar and salt to accelerate oxidation. This works well for steel and iron, producing a rustic black or dark brown patina.

4. Gun Blueing:

Often used for firearms, gun blueing involves applying a bluing solution (like cold blue) to steel, resulting in a dark gray or black protective layer.

5. Paint or Spray Finishes:

For a non-reactive approach, matte black spray paint or specialized patina paints can mimic the look of oxidation while offering more control over the final appearance.

Each method has its advantages, depending on the desired durability, texture, and metal type. Experimentation is key to achieving the perfect matte black or gunmetal patina.