Reddit reviews Easy Mold Silicone Molding Putty for Casting and Jewelry Making, 1/2-Pound

I'm actually about to start casting dice and I've established a decent method of producing the wax models. I started with a blank die (my local game shop sells blanks, you can buy them online if you can't find any local), and I used a silicon food molding putty I found on amazon to make a mold of the blank. From there you fill the mold with wax and you can add your numbers to the wax and then continue from there with the lost wax method.

If you're more comfortable carving the numbers into the dice blanks that works just as well, but it might make the putty mold not come off as cleanly.