There are plenty of ways to polish clay, this is just one put together for this video, but the concepts are the same for other polished plasters, like tadelakt.
You can watch the video at www.youtube.com
Plaster mixes: These mixes vary greatly depending on your substrate, weather, clay, sand, and application. And a test should be made first sampling everything.
First mix fill, or base coat: 1/8 screened clay 1.25 gal 1/8 screened sand 2.5 gal Water 0.75 gal This layer is just to level your base, if your wall is relatively level already you can skip this coat-layer.
Base layer for polish: Clay 0.5 gal Marble sand 1 gal Water 0.5 gal This is the main layer, and most of what makes up the finish. As mentioned in the video, glue can add strength and prevent delaminates while applying the cream layer, also this layer could be applied in two layers if it’s easier.
Cream mix, or clay slip: Clay 1 cup Water 3/4 cup This layer is for filling small pores, and adding clay to the surface, which is what makes it shiny. Oil is what starts to seal, and harden the clay. Wax does the same, and gives the final shine.