Question: To make a concrete sphere.
Options:
Take a spherical shell and spray with oil before pouring in the dry concrete into it. Allow to dry and set. Break the glass shell to remove the concrete sphere.
Take a glass spherical shell and spray with oil before pouring in the mixed concrete into it. Allow to dry and set. Break the glass shell to remove the concrete sphere.
Answer: Take a glass spherical shell and spray with oil before pouring in the mixed concrete into it. Allow to dry and set. Break the glass shell to remove the concrete sphere.