1. Polishing: This is the most common technique for improving the exterior finish of a casting. Polishing can be done manually or with the help of machines. A smooth, glossy finish can be achieved by using polishing compounds and pads.

2. Sandblasting: Sandblasting can be used to remove any roughness from the surface of the casting. This technique involves blasting the surface of the casting with sand particles. This helps to remove any dirt, rust or other impurities on the surface.

3. Shot-blasting: Shot-blasting is similar to sandblasting, but instead of sand, it uses small metal pellets to blast the surface of the casting. This process helps to remove any roughness or irregularities and also helps to create a uniform texture on the surface.

4. Electroplating: Electroplating is a process where a thin layer of metal is deposited on the surface of the casting. This not only improves the appearance of the casting but also provides additional protection against corrosion.

5. Painting: Finally, painting can be used to give a casting a smooth, uniform finish. Painting can be done with various types of paints, including acrylic, enamel, and epoxy. A high-quality paint job can help to protect the casting from environmental factors and ensure its longevity.