First, we dug a hole in the sand. Then O(4), E(1), and I looked for shells and rocks to use to make the face. O and E arranged the rocks and shells in the hole.
Then we mixed up the plaster of paris. We didn't have as much as we needed, but it still worked out fine.
We poured the plaster into the hole and let it sit for more than an hour. Then I lifted out our mask. We were very pleased with the end result.