Polishing concrete countertops is not dangerous, but water and electricity do not mix well. If your stone polishing machine doesn’t have a Ground Fault Circuit Interrupter, be extremely careful to avoid electrocution. Even with a GFCI, it’s a good idea to wear rubber gloves to help insulate yourself.
Wear a particle mask if you’re doing any kind of dry grinding, concrete dust is caustic.

From a single piece of concrete, a range of finishes are available depending on if you polish, and how deep you polish.
Uniform Finish – The concrete has a uniform color, because when it’s being cast, there is a thin layer of cement paste that forms on the inside surfaces of the form work.
Light Polish – As soon as you begin polishing the surface, the thin layer of cement is removed, and the fine sand aggregate is exposed.
Ground Finish – As you polish deeper into the concrete, you begin to expose the larger aggregate in the concrete mix.