1st attempt - I'm using filtered water from a 5gal cooler. The water I used on my first attempt was cold to near freezing out of the spout. After 12 hours the 60% of the outside shell of the form was frozen and crystal clear but not complete.2nd attempt- using above room temperature filtered water, but not hot. Found out that it is possible for bubbles to be trapped in the chin area. Rock back and fourth to remove the bubbles before putting in the freezer.After many attempts... Using cold water works fine. Rock back and fourth to remove possible air bubbles from chin area before putting in the freezer. Skulls should be ready in 24 using cold water. Remove large ice block at the bottom before making a new set of skulls. The rubber mold seems to fit and seal better with the bottom ice block removed. Skulls have a fine powdery finish when removed but are crystal clear.