Lara.......depending on how rough the sink is would determine the type of compound.
The one I had seen done wasn't too bad - just a little dull - they used a polishing compound - although the brand or type I don't know - didn't think to ask at the time. They did use a random orbit buffer on it though.
I would suggest finding an autobody supply shop and asking them. I'd just tell them you have a dull finish you'd like to buff out.......let them recommend from there.........