Take a look at you scene file now, good job on the diamond by the way. I creased the edges in the vertex room on the diamond and repositioned your light, also used the HDRI file from the coronet preset. If you are a new user of Carrara I would review the manual for how to position items in the assembly room and how lights work. Also go through the scene presets in the browser and look at how those scene are set-up and lit and where the camera is placed. The light through transparency was then checked in the render room as well as full raytracing and rendered.
