I used the typical cooler method for directional freezing, and
- Put a clear plastic box with holes drilled in the bottom in the cooler. The holes allow trapped air/impurities to be pushed out below it.
- Put this box on a salsa tub as a riser to keep it off the bottom of the cooler so that the trapped air had somewhere to go.
- Hung a "gold" chain dipping into the middle of the plastic box from the handle of the cooler.
- Let it freeze for about 3 days until it was just below the level of the plastic box.
- Chipped away at the extra ice so that there was just the box, then slid the big cube out of the plastic box.
- Looked good wearing it.