Select a mold for your lantern. Buckets or large plastic ice cream tubs work exceptionally well. Even large balloons work well as a mold.
Fill the mold with plain water, or add a few drops of food coloring to tint your lantern. If you use a balloon, fill it with water then blow some air in it before tying it off. Set the water filled molds outdoors if the temperatures are below freezing, or place them in a chest freezer.
You have to watch the lanterns carefully as they freeze. You want to pour the extra water out of the center after the outer shells have frozen to a 1/2- to 1-inch thickness. The thicker the ice wall, the more durable and long lasting the lantern. Once the wall reaches the desired thickness, pour the water from the center and place a lit candle inside. The flame reflects off the ice and sparkles nicely. Even small cracks and imperfections in the ice become beautiful beneath the warm glow.