Polish the Concrete Form
Once you de-form the concrete, allow a few days for set up before grinding to expose the buried glass. Concrete takes 28 days to cure completely, so the glass is still harder than the concrete that surrounds it, which helps in exposing the embedded glass. For this project, we rented a water-fed grinder. If you use one, move to an area where you can work with water and wear garbage bags as it's a wet process (Image 1).
Start grinding the surface with a 50-grit diamond pad on the grinder, using a circular motion under steady pressure (Image 2).
Be careful as you work around the edges as these can still damage easily. Continue to use the 50-grit diamond pad until the buried glass is exposed (Image 3).
Follow up with finer grit pads, working up to 400- or 800-grit diamond pads. You're trying to create a finished surface that will be smooth to the touch with a matte sheen when dry. If your project has backsplash shelves like ours, save yourself time by not grinding the area where they sit.
Let the vanity pieces cure at least another few days before sealing and polishing