Brushed Stainless Steel.(Image source)

Brushed Copper Sheet.

Galvanized Steel.
(Image source)

Anodized Aluminium. (Image source)

If the item is made of stainless steel, it probably will not need a coating to protect it from corrosion. Usual techniques for stainless natural finishes are brushed bright, satin, and mirror finish. Similarly, metals like aluminium, brass, copper, depending on the situation may or may not require coatings for protection. Different types of natural finishes can be obtained by creating grains on the surface, brushing, and buffing. Aluminium may be anodized in colours.