5 mm squares after they are released from the silicone mold
After the week was up and the concrete was probably 90% cured, I drilled each bead with a .9 mm (.035") metal drill. I drilled from both sides to try and keep the hole centered. The next step was to wet-sand all the surfaces by hand, using a 400 grit sandpaper. This gave a smooth surface to the beads and also got rid of all the surface fibers. To round off the edges (rather than hand sanding such tiny shapes) I tumbled them with steel shot for an hour. When they came out of the tumbler, this is what they looked like among the steel shot:
Tiny square concrete beads in steel shot
The plan is to use these concrete beads in some minimal jewellery designs, such as the partly completed earrings below.
Draft earring design, sterling, titanium, concrete