Clear ice is not made from special water. It is made by controlling which way the water freezes. Let a block freeze from the top down, in a small insulated box with the lid off, and the air and dissolved minerals are pushed ahead of the ice into the last water at the bottom. Cut away that last part and what is left is clear enough to see straight through.
This guide covers the one method that works reliably in a home freezer, two smaller ways to try it, how to cut the block without cracking it or your fingers, and how to put a clear cube into a cut rocks glass so both survive the evening. It sits next to Large Ice and the Rocks Glass, which is about fitting a cube to the bowl. This page is about making the cube in the first place.
Why home ice turns cloudy
An ice tray sits in cold air on every side. Water freezes inward from the top, the bottom, and the walls at once. As it freezes, it pushes out the air and minerals it was holding, and with ice closing in from every direction, they have nowhere to go but the centre. That is the white core you see in a freezer cube. The cracks around it come from pressure, because water expands as it turns to ice.
Camper English, who writes the drinks site Alcademics, described the fix there in December 2009 and named it directional freezing: let water freeze from one side only, and the ice stays clear until the very last part to freeze. In an open cooler, he writes, only the last quarter or so of the block turns cloudy.
Speed matters too. Serious Eats notes that home freezers often push water below 0°C before it starts to freeze, which gives smaller, less transparent crystals. Insulation slows the whole process down, and slow ice is clearer ice.
Two myths to skip
Boiled or distilled water
This is the most repeated tip, and on its own it does not work. In a December 2025 piece for The Conversation, food scientist Paulomi Burey explains that boiling removes some dissolved gas but does not change how the water freezes, so a tray of boiled water still turns cloudy in the middle. Distilled and filtered water behave the same way. Serious Eats tested boiled, double-boiled, and distilled water in trays and reported cloudy cubes every time. Use ordinary tap water if it tastes good to drink. If it does not, filter it for taste, not for clarity.
Silicone sphere moulds
A standard sphere mould looks like a bar tool, but it freezes from the outside in like any tray. You get a round cloudy ball. Some moulds are built for directional freezing, with an insulated jacket and a reservoir underneath for the cloudy water. Those can work. A plain silicone sphere will not.
The cooler method, step by step
You need a small hard-sided picnic cooler that fits in your freezer with the lid off, a serrated bread knife, a clean towel, and a cutting board. A cooler of a few litres is enough for a week of rocks pours.
- Fill it partway. Rinse the cooler and fill it with cold tap water to a depth of about 7 to 10 cm. Deeper water gives a taller block but takes longer to freeze.
- Freeze with the lid off. Set the cooler level on a shelf, away from the fan if you can, and leave the top open. The open top is the only way the cold can get in, which is the whole point. Do not move it while it freezes.
- Check early. Guides give a wide range, from about 18 hours to two days, because every freezer and cooler is different. Start checking at around 18 to 24 hours. You want a solid clear slab on top with some liquid water still underneath. Note the depth and time that worked.
- Release the block. Let the cooler sit out for a few minutes, then turn it upside down over the sink or a towel and let the block slide out. Run lukewarm water over the outside of the cooler if it sticks. Never pour hot water on the ice itself. If water is still trapped inside, it will run out when you flip it. That water holds the air and minerals you wanted to get rid of.
- Trim the bottom. If the block froze all the way through, you will see a cloudy layer on what was the bottom. Cut it off. The clear part is what you keep.
Without a cooler
Any insulated container with an open top follows the same rule. The Conversation piece suggests an insulated mug for a single block, and a vacuum-insulated food jar should behave the same way. Smaller containers freeze faster, so check sooner. Commercial clear-ice trays do the same thing at a smaller scale: an insulated case around small moulds, with a space underneath where the cloudy water collects. They cost more and make fewer pieces, but there is no knife work.
Cutting the block into cubes
Clear ice cuts best by scoring and snapping, not by sawing straight through. Let the block sit out for a few minutes first. Ice straight from a very cold freezer is brittle and shatters in unexpected directions.
- Lay a damp towel under the cutting board so nothing slides. Hold the block with a folded dry towel, never a bare hand, and wear cut-resistant gloves if you have them.
- Saw a shallow groove where you want the break, a few millimetres deep, along the full width of the block.
- Set the knife in the groove and tap the back of the blade once, firmly, with a wooden spoon or the heel of your hand. The block should split along the line.
- Cut the slab into strips, then cut the strips into cubes the same way.
Japanese bartenders made a craft of this step. In a 2019 history of sphere ice for PUNCH, Cocktail Kingdom founder Greg Boehm says ice balls were made by hand in Japan through the twentieth century, a habit that later travelled back to bars in New York. Bartenders trained in that style work with an ice saw, an ice knife, and picks, and carve more than spheres. At home a bread knife and a clean square cube are enough. The patience is the part worth borrowing.
How big a cube for a rocks glass
Size the cube to your glass, not to a number from the internet. A product listing gives capacity in millilitres, which tells you how much liquid the glass holds, not how wide the bowl is inside. Measure the inside of the rim with a ruler, then cut cubes about a finger's width narrower. The cube should sit flat on the base with a ring of air around it and its top below the rim, so you can pour whisky around it.
Cut one cube, test it in a dry glass, then cut the rest to match. If it catches on the way in, trim it. Never push a cube into cut glass. A jammed cube is a common way for a rim to chip from the inside.
Storing clear ice
Ice picks up smells from the freezer. Once the cubes are cut, put them back in the freezer on a tray for half an hour so their surfaces set, then move them to a lidded container, with baking paper between layers so they do not freeze together. Keep them away from onions, garlic, and open food. A cube left loose for a week can taste of the freezer.
Frost on the surface hides the clarity. A quick rinse under cold water just before serving takes it off.
Putting a clear cube in a cut glass
Clear ice that comes straight from the freezer can crack the moment it meets room-temperature whisky. Serious Eats points out that a very cold clear cube cracks on contact with a warm spirit, which is why bars let it temper. Leave the cube on the counter for a few minutes, until its surface looks wet rather than frosted. It will still be hard and cold, but it will not crack as easily.
- Chill the glass first if you like. Should You Chill Whisky Glasses covers when it helps.
- Lower the cube in by hand or with tongs so it lands flat on the base. Do not drop it in. Cut glass is a scored wall, and a falling cube is how a facet chips.
- Pour the whisky down the side of the glass, not onto the ice from a height.
- When you finish, tip the ice into the sink. Do not leave it to melt in the glass overnight. Wash the glass by hand and dry it. How to Care for Cut Glass has the full routine.
What clear ice changes in the glass
Some of this is about the drink. The Conversation piece notes that clear ice is denser and melts more slowly than cloudy ice, and that it carries fewer stray flavours from the freezer. Any large cube already melts more slowly than a handful of small ones, because less of its surface touches the whisky. Clear ice adds a cube that does not crack apart into small, fast-melting pieces once it is in the glass.
The rest is about light. A cloudy cube is a white block in the middle of the bowl. A clear one lets light through. In a cut rocks glass, low side light passes through the facets, then the ice, then the whisky, and lands on the table as a moving patch of amber. You can see the cut on the far side of the glass through the cube. The object is still. The light is doing the moving.
Clear ice is not required. A freezer cube still cools the pour, and neat is a serve of its own. If you want cold without water, Whisky Stones vs Ice sets out the trade. For a longer drink, the cloudy trimmings are ideal for mizuwari or a Japanese highball.
A few common questions
Why is my ice cloudy?
Because it froze from every side at once and trapped air and minerals in the centre. Freezing in one direction fixes it.
Does boiling water make clear ice?
Not on its own. Boiling removes some gas, but water in an ordinary tray still freezes from the outside in and still clouds in the middle.
How long does clear ice take to freeze?
Often 18 to 48 hours in a cooler, depending on water depth, the cooler, and your freezer. Check early and stop while some water is still liquid at the bottom.
Can I make clear ice without a cooler?
Yes. Use any insulated container with an open top, such as an insulated mug or food jar, or a clear-ice tray built for directional freezing.
Why does clear ice crack in the glass?
It is very cold and meets a warmer drink. Let the cube sit out for a few minutes until its surface looks wet, then add it.
Glasses for one clear cube
- Smoke Orb Whisky Glass: 320 ml, a grid of asa-no-ha lattice and faceted dot panels over a thick clear base.
- Cobalt Deep Whisky Glass: 300 ml, yarai deep diamond cuts from rim to foot, with clear crystal in the grooves to read the ice and the pour.
- Smoke Cloud Whisky Glass: 360 ml, an asa-no-ha band and tall petal facets, with room for a large cube and a short pour.
Each of these listings is Edo Kiriko: handmade crystal, hand-cut in Tokyo, as its product page states. Measure the one you choose before you cut your cubes. View all glassware in Whisky Glasses.
Related reading: Large Ice and the Rocks Glass · How to Serve Whisky in a Rocks Glass · How Tokyo Bars Serve Whisky in Glass