The following effect came from trying to layer watered-down gesso on top of oils. The result was a great texture that almost reminded me of hail.
So Moses lifted his staff toward the sky, and the Lord sent thunder and hail, and lightning flashed toward the earth. The Lord sent a tremendous hailstorm against all the land of Egypt. Never in all the history of Egypt had there been a storm like that, with such devastating hail and continuous lightning. It left all of Egypt in ruins. The hail struck down everything in the open field – people, animals, and plants alike. Even the trees were destroyed. The only place without hail was the region of Goshen, where the people of Israel lived. Exodus 9:23-26