Clear ice, and whether it's worth it

Water in an ice tray freezes from all sides inward. Dissolved air and minerals are pushed ahead of the freezing front and end up concentrated in the middle, where they form the white core you see in every home ice cube. Cloudiness is trapped air and impurities, not dirt.

Boiling the water first helps slightly, by driving off some dissolved gas, but it does not solve the problem — the freezing direction is what matters.

The trick used by bars is to make the water freeze from one direction only, so the impurities are pushed to one end rather than to the centre. At home the usual method is an insulated container — a small cool box left open at the top — placed in the freezer, so cold reaches the water mainly from above.

The top two-thirds freeze clear; the bottom third traps everything and comes out cloudy. Cut that part off and you have clear blocks. It takes 18-24 hours and a bread knife, and the cutting is the fiddly part rather than the freezing.

Mostly, no. The honest answer is that clarity is aesthetic. What genuinely changes the drink is size and density: a single large cube has far less surface area than the equivalent volume of small cubes, so it dilutes a spirit-forward drink more slowly — and a large cube from a mould works for that regardless of whether it is clear.

Clear ice does melt marginally more slowly than cloudy ice of the same size, because trapped air pockets create weak points. The effect is real and small, and it is not the reason to do it.

So: if you want your Old Fashioned to look like a bar's, make clear ice. If you want it to taste like a bar's, make it big and make sure your freezer isn't full of anything strongly aromatic — ice picks up smells readily, and that is a far more common problem than cloudiness.