I love to work with concrete. It´s so versatile and easy!
The only thing is you have to have patience, well... I´m not very good at that :-)
Anyway I made a batch of place cards out of concrete. You won´t imagine how easy that is.
All you need is:
icetray in any shape
Follow instruction from my previous post and mix your concrete.
Fill the concrete mix in the icetray and now: wait.
At least 24h before you get the pieces out. Trust me.
Once it is dried, get the pieces out and sand if necessary; or you just stick with the rough look, whatever you like. Now you can write or scribble on them, I used a white chalk marker so the place cards will be reusable.