What kind of resin for polymer clay?

I made a pendant of silver and polymer clay. The polymer clay has an image on both sides which I’d like to protect. What kind of resin should I get, how do I apply it and how do I use it (curing etc). I used a heat gun to get rid of bubbles the only time I worked with resin years ago and don’t remember much. The image is not in a bezel so there isn’t much of a rim to hold it in at all. It’s pretty flat.