This was one of my first worthwhile pieces learning to work with resin. I pretty much just used layers of epoxy resin and rhinestones to create symbols. My techniques have since improved, but this remains one of my favorites.
I used a fairly shallow metal bezel with clear 2mm rhinestones to make the bottom layer. I made a Pi symbol with 2mm blue pearl rhinestones in the next layer. The last layer is just another layer if epoxy resin for the doming effect.
I highly recommend taking up resin casting if you haven’t tried it yet. I’ve begun incorporating resin in a lot of my projects. You can buy bezels or make your own using bottle caps, polymer clay, or sheet metal. Both epoxy and polyester resin can be used in molds too, just remember to use a mold release agent Transparent and opaque dyes as well as effect powders are available for resin. Try embedding small objects such as stickers and watch parts in layers to create a unique pendant. Have fun!