Insert mold polishing

Hi,

I am a machining student and currently working on a mold project. I am at the point of using diamond paste on the mold inserts for polishing. We watched a video in class, but it has been a couple of weeks. I have 2 questions I am a bit unsure.

For each grit does a person usually stop when the finish is without streaks, or more a consistent color. The intent at the finest grit is for a mirror finish. We are to use 220, 400, 600, 800 and 1200 grits.

Should I use oil mixed in with the paste? I have found recommending of both with and without.

We can work on this part of the project at home, so I am working on it this weekend

Thanks, Brian