Does Refreezing Clear Air-Free Ice Result In a Large Clear Block?
November 05, 2010
This is an experiment in my ongoing project to make clear ice. I've figured out a way to do it using an Igloo cooler. This experiment is an attempt to make clear ice without one.
A long time ago, I tested the theory that freezing, thawing, and refreezing water makes clear ice blocks. After 13 tries I determined that it refreezing water does not make clearer ice.
However, it recently occurred to me that I could test out something else. If we take just the clear part of ice (leaving behind the cloudy, air-rich stuff), melt it and refreeze it, will the new ice be clear?
A bar in San Francisco refreezes their Kold-Draft cubes. One bartender told me he thought it makes clearer ice than with just tap water, but still not completely clear.
If this experiment works, then someone anyone could refreeze small bits of clear ice into large blocks. Efficient? Nope. But interesting.
(Oh, and long story short: this experiment was inconclusive. Don't want to make you read if you're not into it.)
Anyway, step one was to make clear ice, as I do using the Igloo cooler method. I made two partial blocks of ice. I let the water freeze in the cooler, then knock off the thin skin that forms around the bottom of the cooler (full of water).
Then I took these two clear slabs, broke them into large chunks, and put them into the cooler to melt.
After it melted, I refroze it.
The ice in the picture above is upside-down from how it was in the cooler. Here's a closeup.
At first view, it looks a little cloudy in the middle of the bloc- but I think that's because I had to move my refrigerator a couple of times during this process and jostling the container does seem to make cloudier ice.
Looking just at the cloudy part at the bottom end (top in the picture above), I can't really say whether it's less cloudy than it is with regular tap water. This experiment is inconclusive.
My theory is that as the water cools down or warms up to room temperature it reabsorbs a standard amount of air, and this experiment won't work. However:
If I repeat this experiment (and I probably will), I should:
- Make the clear ice as normal, but not break up the slab into chunks. This saved time but probably adds air.
- Use more refrozen water in the cooler when refreezing. Here is was a little too hard to tell what percentage of ice was cloudy, so I could not compare it with the time I did this experiment with regular water.
The icesperiments continue!
An index of all of the ice experiments on Alcademics can be found here.
It's safe to say that the unfrozen water you had left in the block had a higher concentration of air and impurities then the water you started with. Have you though about draining that water and then refilling it with fresh water? You can probably just put the cooler back over it and allow it to freeze upside down so it freezes from the bottom up. Then after a bit more has frozen you could do it again.
Posted by: Gael | November 05, 2010 at 01:02 PM
Another great idea for an experiment. Thanks again Gael!
Posted by: Camper English | November 05, 2010 at 01:04 PM
So I've come the conclusion that you must have 3 things for clear ice.
1.) It must freeze slowly so impurities don't get trapped.
2.) It needs to freeze in a particular direction in order for those same impurities to go somewhere.
3.) You need an expandable container so it won't crack as it freezes.
Most freezers are way below the freezing point so they'll freeze pretty fast. We could take care of the 1st one by changing the temp of a freezer but that wouldn't take care of 2. Insulation would keep the cold temp from penetrating too fast and encourage a direction. But you can't use a dewar or else it would crack. So basically the best possible solution is what you have found because a plastic cooler is flexible.
I came to this conclusion after reading about a neutrino experiment in Antarctica.
They need 2 meter by 1 meter blocks of ice that are completely clear. They freeze in an environment well below the freezing point as well. The way they get around it is by freezing the block for two months from the top down. They have a couple other things like a Freezer Control Unit which is basically a computerized heater and a membrane contactor which filters out air from the ice.
I assume you're fine with 10% cloudy ice so you don't need a membrane contactor and you could probably also live without the FCU since it's overkill. What we're left with is your ingenious solution.
I'll consider this more or less solved and I'll just go back to my mundane studies on nanopores.
Posted by: Gael | November 05, 2010 at 01:38 PM
Thanks Gael- Awesome comment once again. I hadn't really considered either the fact that my container is expandable or that I am luckily that my freezer isn't terribly powerful so the whole thing goes slowly. I still have ambitions to try a blast freezer though...
Posted by: Camper English | November 07, 2010 at 07:52 PM
I've been able to make pretty clear ice, but only in small cubes.
1. use distilled or brita water (air will stick to impurities)
2. bring the water to a boil in a sauce pan (the activity releases remaining air, while the temperature of the water means it will freeze slower)
3. use a silicone ice tray (if you don't fill it up all the way the cubes will have room to expand upward
4. in order to get the cubes freezing from the bottom up (so the air can escape while they freeze), place the tray in a caserole or baking pan with enough water to cover 1/2 the ice cube tray. If you salt the water, it won't freeze, but the temperature of the water in the pan will be the same as the air in the freezer but conduct better, so the bottoms of the cubes freeze sooner.
Of course, you kind of have to be a total tool to go through all this, but it looks pretty great in a glass of bourbon.
Posted by: Horst | November 07, 2010 at 08:48 PM
Camper - I just want to let you know that I will never get tired of reading nerdy posts about ice...
I haven't done any experiments yet, but my freezer is pretty effing high-powered and is constantly at -8F. I bet this is going to cause problems, huh?
Posted by: Rick | November 09, 2010 at 09:00 AM
Thanks Rick. I actually would love to try a super cold freezer to see if it's a bad thing. As Gael pointed out, fast freezing supposedly traps air and impurities, but I wonder how fast...
Posted by: Camper English | November 09, 2010 at 11:04 AM
The science has been done on that.
The abstract says if you freeze faster then 2mm/min then you get a lot more trapped air. If you freeze at 0.5mm/min you get 6 bubbles/mm^3 and it you freeze at 5mm/min you get 300 bubbles/mm^3. If you want to download the paper you probably need to pay for it but I could email the pdf to you if you want.
Posted by: Gael | November 09, 2010 at 12:28 PM
Just to hammer the point home I found another document that says slow freezing is key along with removing dissolved air.
Posted by: Gael | November 09, 2010 at 01:05 PM
I may give a few of these things a try. Thanks!
Posted by: Camper English | November 10, 2010 at 02:58 PM
If it's worth trying, I remember Heston Blumenthal in "In Search of Perfection" using a vacuum to expand chocolate. He punctured a piece of tupperware, slipped it into a space-saver bag with a one-way vacuum valve, aligned the valve and the puncture, and walah!, DIY vacuum pump. It seems like that would get some of the air out. It makes me wonder if ice in Denver is clearer than ice in Miami.
My other idea is to spin the ice as it freezes. Seems like the slow-crystal formation that leads to clear ice is partially the result of low-churning. When you added kinetic energy to the block, it was cloudier bc of the churning, right? Maybe spinning would prevent that churning. I'd think ice formed in a centrifuge'd be clear. Maybe something as simple as fixing the cooler to a record-player turntable? You might could even turn it on it's side to see what happened . . . It'd be a cool story, anyway, and maybe the resultant ice would look flashy.
Posted by: Christopher Youngblood | November 11, 2010 at 12:55 PM
I am not positive what you mean by "low churning" but I think that might be the dynamic of freezing ice and how it churns just as it begins to freeze. If so, I just read about this in the book Ice by Mariana Gosnell and it happens in lakes too- lakes that freeze clear.
Regardless, a centrifuge of that kind maybe could do the trick, as ice is less dense than water and might move more easily to the outside of the freezing vessel...
Posted by: Camper English | November 11, 2010 at 02:10 PM
I am really enjoying reading this blog.
Ice is a bit of a passion of mine as well. My girlfriend is sick of hearing it... but my name means "ice" in Japanese.
Here are some of my results:
Ice from a Tovolo king cube tray (not insulated)
This is what I got from the Coleman Cooler (I let it freeze all the way down)From Ice
I have some ideas on making custom ice cubes and will have the results in my photo album.
Thanks for the inspiration!
Posted by: Cory Hain | February 03, 2012 at 11:32 AM
Wow, did you get no cloudiness at all, or did you cut it off before taking these pictures? I've never had ice that clear unless I didn't let it freeze all the way.
Posted by: Camper English | February 03, 2012 at 11:41 AM
I don't get cloudiness. Occasionally air streaks and bubbles (you can see two in the Tovolo cube).
I don't need to cut it, I thought I would but it never got cloudy in the bottom of the cooler so I decided to let it freeze all the way down.
Posted by: Cory Hain | February 03, 2012 at 11:56 AM
That's pretty odd - most everybody's ice is cloudy. What is your water source? Do you treat/filter it any way?
Posted by: Camper English | February 03, 2012 at 12:14 PM
We have an Aqua Pure Reverse Osmosis Filter.
I get the water from the tap and do not boil it.
It doesn't seem to me that impurities in water are a major contributor to cloudy ice. I have seen very nice clear ice on a lake that I would not want to drink from.
That being said, Portland Bull Run water is pretty nice.
Posted by: Cory Hain | February 03, 2012 at 01:39 PM
Here is the experiment that I did by shaking as much air as I could into the water before freezing it. I am boiling it next to see if I can remove all of the bubbles. The final step is when I get my vacuum chamber set up for making silicone ice molds. I will put the water under vacuum for 10 minutes to see if that works. (it nearly boils at room temp when I have done that)
Here is a medium size ice block with air bubbles (still not cloudy):
These are smaller blocks:
Do you use hard water when you make your ice?
Posted by: Cory Hain | February 04, 2012 at 11:26 AM
You sir, have the clearest ice in all the land, even when you try not to. All you ice comes out clear, no matter what ice cube trays/mold you use? If it's not your reverse osmosis filter then I don't know what sort of magic you have. Most people are starting from much cloudier ice to get clarity; you are starting from clear and trying to get clearer. I have ice envy.
Posted by: Camper English | February 04, 2012 at 11:47 AM
Here is what I got from boiling the water. Smaller bubbles.
I got my vacuum equipment set up and tried to make ice under a vacuum. It was very interesting. I used filtered water and it boiled at room temperature under the vacuum. I kept in vacuum while freezing. Instead of freezing, the water supercooled. When I hit the container with my finger... it froze in about 10 seconds. I guess there were very few impurities for the ice to nucleate on. My sense is... supercooling never leads to clear ice, regardless of impurities. Imperfection seems to override impurities.
Posted by: Cory Hain | February 11, 2012 at 03:56 PM
Posted by: Cory Hain | February 11, 2012 at 03:57 PM
Posted by: Cory Hain | February 11, 2012 at 03:58 PM
Posted by: Cory Hain | February 11, 2012 at 04:01 PM
I have been following Camper's ongoing quest for the perfect ice cube from day one. In about 5 weeks, I will be able to try my hand at making the perfect ice (I'm moving). All I can say If I can make ice a clear as Cory's (I won't be using the local water from Lake Mead) I will invite Camper over for an ice making party!!
Posted by: Tony Lepore | February 12, 2012 at 01:42 PM
Wow you can use that as a magnifying glass.
Posted by: Camper English | March 03, 2012 at 07:31 PM
Here is the secret to clear ice:
The pictures you see come from a dorm room style refrigerator with the partition between the ice box and the main compartment. It creates a 2 zone temperature differential. The upper zone is around 27-31 degrees. Below the glass shelf where the tovolo ice tray sits is about 2 degrees warmer. This creates automatic directional freezing that avoids super cooling.
That being said... Air is still an issue. Boiling can help but it is not consistent. Degassing by letting it sit overnight works a bit better. Boiling the water in the tovolo trays works well. It avoids re-introducing the air through pouring. Since I cannot buy a bunch of small fridges, I moved my testing to a 20 cubic foot freezer. This involves using an external thermostat (like they use in keg-o-rators). I have set the temperature to 29 degrees. I am starting to see less bubbly ice but because freezing in such a large space is not directional, the water does not freeze from top to bottom. I am making custom silicone trays with a small amount of insulation.
The tovolos are taking about 4.5-5 days to freeze. I have compared them to clinebell ice. They seem to have a much slower melt rate. That is a pretty unscientific observation but it would make sense since slow freezing would produce a much denser crystalline structure.
(I wrote this about 3 months ago... and have since then figured out how to de-gas much better during freezing. The methods I have figured out are perfect for clear silicone molded ice)
Posted by: Cory Hain | May 25, 2012 at 04:09 PM
Here are some notes about your comment:
>>At first view, it looks a little cloudy in the middle of the bloc- but I think that's because I had to move my refrigerator a couple of times during this process and jostling the container does seem to make cloudier ice.<<
This is because it is supercooled. Your freezer temp is too low. Put an unopened bottle of distilled drinking water in your freezer and check it in several hours. You will notice that it is still liquid. Pull it out and shake it... notice what hapens. That is the primary reason ice is not clear from the freezer.
Your method involves insulating the water so it stays closer to freezing and does not super cool until the end when the thermal mass of the remaining liquid water and insulating container can no longer keep it close to the freezing point.
check out this youtube video youtube(dot)com/watch?v=fSPzMva9_CE
Posted by: Cory Hain | May 25, 2012 at 04:19 PM
Awesome - thanks, I didn't realize it was hovering near the freezing temperature. I haven't been able to do that at home since my freezer doesn't give me much control. Sounds like you've been spending a lot of time on this!
Posted by: Camper English | May 25, 2012 at 08:34 PM