Here are a couple of notes and pictures on the second piece that I made.
Design-wise, this is a much simpler piece (since it is flat) and the mold is relatively simple (compared to the one for the Desk Lamp)
I integrated the bearing and some support structure into the model before pouring the concrete (that way I didn't have to worry about drilling holes into the piece afterward)**
** I live in an apartment building and I can not use a lot of noisy tools (like grinders, sanders, drills, etc). So I have to come up with ideas to make the piece in a way that not much after-work is required. That is the reason for all those different things that you see on the mold to hold together the bearing.
mold base
added glass pieces
added bearing
final piece
The concrete mix I used for this one is the same as the Desk Lamp
For the reinforcement, I use a decorative metal screen cut to desired sizes (note that having holes is preferred)
The glass pieces are known as "fire glass" and people usually use them to decorate fire pits
I got the Lazy Susan ball-bearing from Amazon (I am guessing they can also be found in hardware stores)
I seal the piece with food-safe sealant