This is polished the surface.

5. When the plaster dries, it will need to be wiped with sandpaper with a granularity of 400, and then wipe with a wet rag. After you need to go again with sandpaper, but this time with a grain of 600. This is polished the surface. The higher the granularity, the more contrast. And after the second passage with sandpaper, wipe the wall again with a damp cloth.