This is a post Sean and I have talked about making for months and months. I don't think it would be an exaggeration to say his inbox has at least 40-50 emails on the topic and probably twice as many pictures. He responded to a lot of those emails with his own ideas, suggestions, photos, etc...so look for him to update these posts as well. Fortunately a lot of what we covered has been done elsewhere, no need to completely rehash what others have already figured out. Before continuing any further I want to acknowledge Camper English's Alcademics blog as a major source of inspiration on all things ice and a worthwhile read on any given day for the booze-minded.
Rather than walk through the numerous experiments Sean and I have tried in the pursuit of clear ice I'm just going to list a few highlights and techniques which I have had success with.
Using a cooler to make ice as discussed on Alcademics is really the way to go. The whole principle, as I understand it, has the concept of directional freezing at it's core. Cloudy ice is the result of air that can not completely escape from the water as it freezes*. Since clear ice block making machines are way too expensive and massive for home use (though who doesn't want a Clinebell in their basement?) employing directional freezing will allow someone to make clear ice at home for just a few bucks.
If you take the top off of a cooler, fill it with water, put it in the freezer and wait a couple of days you will end up with a block 1/2 to 2/3 of which is crystal clear (there may be a small string of bubbles in the clear section but the cloudy portion is concentrated at the bottom). Since the sides and bottom are insulated the water freezes from the top down and the air collects in the last 40% or so before it freezes. I usually try and remove the block from the cooler prior to that last section freezing. It's a lot easier to chip off that part and drain the water that hasn't yet frozen. But let's get real, if you do this regularly there will be plenty of times when it gets all frozen before you have the time to deal with it. No big deal, the cloudy part chips off easily, it just takes a little bit longer.
What's all this got to do with foam panels? Well, if you're like me and trying to do these experiments on the cheap then you probably have a cooler from a thrift store that cost about $3-$4. I've tried making ice with 3-4 small to medium sized coolers and some of them don't let go of the ice so well. I have a Rubbermaid model that works like a dream. Take it out of the freezer and let it sit on the counter for a minute or two, flip it over and give it a shake, then out slides an awesome chunk of ice. But that cooler is the exception. Other ones I've used have required a lot more effort and fairly ridiculous techniques (sliding multiple spatulas between the ice and the liner) to facilitate the removal of the ice. Those coolers are a pain. But I hate throwing things out.
So then...foam panels. If you're dealing with a cooler that won't let go of the ice try prying the liner out with a screwdriver. Yeah, you'll mess up the plastic/insulation but that's fine. You'll end up throwing that section away eventually (unless you don't like throwing away things either). The liners are usually glued at the bottom and sometimes on the sides too. Once you have the sides somewhat freed get a good grip on a section and wrestle the liner our. That step is also a pain but you only have to do it once. Or just find some other box shaped container you want to use for ice.
Hardware stores sell foam insulating panels that are handy for this sort of thing . The one I used was about $12 for an 8'x2' sheet. Cut the panel down to fit the sides of the liner. Cut another one for the base but include the extra area added by the panels on the sides. An 8x2 piece will make a lot of panels.
Fill the liner with water, secure the sides with a bungee cord, or rope or whatever and slide the thing into the freezer. You'll know it's frozen when you see that the liner is no longer resting flat on the base. Pop the panels off, run it under cold water** for a few seconds and it should slide right out. I'm guessing you could use these foam sheets for pretty much any size container though they should probably be food grade. The main limitation is likely going to be freezer space.
As you can see, I didn't get this one out of the freezer before it froze all the way.
The air section chipped off fine though.
*Kevin Liu breaks down the science going on along with another technique using a modified dorm fridge here.
**Cold water is still warmer than ice. I used to use warm water until it cracked a large portion of the clear ice. There's just no need. Cold water works fine.