Do I use cerium oxide with the smoothing pad?

No.

Our smoothing pads are a diamond disk that will grind your glass.

Cerium is used for polishing your glass. It is generally used with a carrier that has no grinding or polishing ability unto itself, like the Synthetic Felt, or LP66 material.

All you need to use with our Smoothing pads is water. They will give you a "pre-polish" finish from which you can use cerium oxide and a polishing pad to obtain your polish.