This technique to freeze a bottle inside an ice block uses directional freezing (freezing inside an insulated cooler with the top off so that it only freezes from the top-down), with the bottle raised high so that it's in the clear part of the ice block.
Another method of making super clear ice spheres using different molds in a cooler.
I did a podcast interview with Brian of Bartender Journey and it's now online. Thirty glorious minutes of me talking about things I often write about. But out loud! Check it out here. I come in at around the six minute point.
There is a new clear ice ball maker on the market, so I gave it a test run.
The short answer is: Poke holes in the tray and set it on a riser at the bottom of an insulated cooler. The long answer? Read along.
Commercial ice machines like the Clinebell freeze blocks of clear ice by freezing from a cold plate on the bottom, while a water pump near the surface keeps water circulating (thus preventing ice from forming on the surface). An Alcademics reader wrote me to tell me about a method he developed that sort of combines these two methods for the home user, producing a mini-Clinebell-type block.
I tested a method of making clear ice balls at home. It works just fine.
A book on cocktail science theory and practice that I highly recommend.