First, let me define what I mean by fracture. I’m talking about a crack in the inside of your ice that may or may not extend all the way to the surface (usually, they do) So we’re not talking about broken ice, but ice that might be broken soon, because it’s weakened by the fracture(s). Fractures are a part of ice carving that you usually try to avoid, but even if you do everything right, they’re going to happen at times, so you should know some ways to deal with them.

   

Why they happen

    Most fractures are the result of thermal stress on the ice. When you take a block out of the freezer, unless it’s insulated, the outside of the ice is suddenly exposed to warmer temperatures while the center of the block is still at the freezer temperature, which might be as low at 20 degrees F below zero. So from the center to the edge of the ice, you have a temperature differential or gradient where the ice temperature goes from very cold at the center to melting at the edge. Often, the structure of the ice can’t handle this differential, and to release the stress, the ice will fracture internally. When I’m explaining it to people who have never carved ice, I usually ask them to think about what happens when you drop a very cold ice cube into a warm glass of water.

    If you try to cut into a block that may be on the verge of fracturing, then you’re adding physical stress to the thermal stress and the odds of a fracture are much higher. Also, consider that when you cut into a block, you’re suddenly exposing that cold ice in the center to warm air and warm tools. Ice can also be fractured by pure physical stress, such as when you accidentally smack a sculpture into the edge of the freezer doorway. If you don’t completely break part of the sculpture off, you might be left with a slightly fractured sculpture.

Why you want to avoid them

    There are two reasons to avoid fractures: they can detract from the look of your sculpture and they can weaken a sculpture. Fractures are usually quite irregular and they change the direction that light moves through your sculpture so they can really stand out visually. And because they’re generally in the center of the ice, they don’t disappear during the event. If you had a logo sculpture and a fracture line went across the logo, you might have an unhappy client, depending on how noticeable it is. I’ve also wondered before how a newly married couple might react to a heart sculpture with a large fracture through the center. Fortunately, for me that’s never come up. Also, if you have a fracture through an important structural portion of your sculpture, the sculpture might actually break if the surrounding ice isn’t strong enough. With fractures that are mostly horizontal, this is rarely an issue, but vertical fractures can present a real problem. When I carved on Junichi’s team in Alaska, there was a fracture in a bad spot on our sculpture. To deal with it, Junichi actually went ahead and broke the piece completely off and then froze it back on so that that part of the sculpture would be strong enough.

Avoiding fractures

    Few people start carving ice in the freezer, so one of the first things many carvers learn is to properly temper their ice. When you temper your ice, you’re allowing it to adjust to the temperature you’re carving at slowly enough to avoid fracturing. Usually this involves keeping the air off your block by putting a plastic bag over it when you take it out of the freezer and allowing the block to sit undisturbed for a couple of hours. If you’re using a Clinebell block, then you can leave it in the box. If a walk-in refrigerator is nearby, letting your ice sit in there for several hours (even overnight) works well, especially if your freezer is very cold.

    Your ice is completely tempered when its entire surface is wet: not when it’s flooded the floor with meltwater and is about to fall over, but when the surface no longer has any dry frozen spots. This usually takes one to two hours at room temperature. There are advantages to carving blocks that aren’t completely tempered, but if you want to practically eliminate the possibility of a fracture, wait for the block to temper completely before you carve.

    If you carve inside a freezer or outside in below freezing temperatures, then you have a completely different situation. When there is little difference between the ice temperature and the air temperature, YOU DON’T NEED TO TEMPER YOUR ICE! I’ve been asked a number of times how I tempered my ice when I carved in my freezer studio. No tempering is required, you can just start carving because the ice is carved at the same temperature that it’s stored at. (In my case, about 18 degrees F)

    If your block is not completely tempered, oftentimes you can still carve it without significant fractures occurring, but you have to be careful. In fact, you’re using a paper template on your ice or if you’re going to be welding pieces on to the sculpture, you want to start carving early. Experience is required to avoid fractures, but the basic rule is that the further you stay away from the center of the block, the better things will go. So if you are using a paper template on the block, you could trace the design with a die grinder first instead of immediately cutting into the block with a chainsaw. And if you’re freezing excess ice back on to the carving to make it larger, then if you can get the excess ice from the edge of the block then you’re less likely to end up with fractures.

    If you’re cutting into a cold block with a chainsaw, the ice will usually give clues that it’s about to fracture. If you can see tiny cracks occurring ahead of your chainsaw cut (if your saw is chasing cracks), then you’re risking a fracture. Also, often you can tell how delicate your ice is my the sounds it’s making. More on this another time.

    The direction you cut into the block also makes a difference. Plunging your saw into the face of the block (you could envision cutting out the center of the letter “O”) puts the most stress on the ice structure. On the other hand, splitting a block (cutting parallel to the 40”x20” face of the block resulting in slabs of ice) rarely results in fractures (see illustration below.)

    Tools other than chainsaws can cause fractures also. Any hot tool, like an iron or warm aluminum plates for welding, can cause fractures in ice that’s too cold. Applying heat to ice becomes risky when the ice is colder than about 15 degrees F.

   The thickness of ice makes a difference. Thick pieces of ice have a long distance from the outside to the center, and the longer this distance, the greater the risk of fracture from temperature changes. Thin pieces of ice adjust to temperature quickly and fracture less frequently.

    Finally, the type of ice makes a difference also. “Can” type ice blocks  are less likely to fracture than Clinebell blocks. This has to do with the direction of freezing during production of the blocks. Clinebell blocks freeze in only one direction, while “can” blocks freeze in five different directions (more on this another time.) Clinebell blocks are particularly vulnerable right after they’ve been harvested and I usually wait at least a day before carving them. (Mike Clinebell has provided an explantion for this situation below, as well as pointing out some poor spelling on my part, (sorry about that)). Clinebell blocks carved too early, if they don’t fracture throughout the block, will frequently get small edge fractures that can be annoying if you’re carving a logo.

Fixing fractures

    The bad news is that you can’t really “fix” a fracture. If the fracture is a structural concern, then you can cut it out and reweld or break the sculpture at the fracture and refreeze it. If it’s a real appearance problem with a logo or something, you may have to recarve part of the sculpture. You might be able to hide a fracture with detailing or even snowfilling. Often, however, your best bet is to make sure you don’t fracture your next sculpture (unless you’re trying to.) Many times, fractures are acceptable and even unnoticeable as long as they don’t compromise a vital part of the sculpture.

Fracturing ice on purpose

    Sometimes you want ice to fracture, mostly for effect. For a large “icy” looking display piece recently, I went out of my way to fracture the blocks as much as possible. To ensure that the structure of the piece wasn’t compromised too much, I welded the fractured ice to intact ice, resulting in extra-thick, cracked up blocks. An added bonus was that the cracks never faded, even though the sculpture was out for several hours, then stored in a freezer, then displayed again for several hours.

    To fracture the blocks for this piece, I took cold blocks and dumped warm water over them. One block was surprisingly stubborn and just would not fracture after several attempts. Finally, it popped into the most fractured block I’ve ever seen.

    Master ice sculptor Robert Bifulco once related to me a familiar story. He took a finished sculpture out of the freezer and unfortunately, it popped while he was readying it for the event. I might be missing some of the details, but the end result was that he didn’t have time to really fix the sculpture, and he went ahead and put it out. The client loved the piece and asked how he managed to put that neat cracked effect in the ice!

The following comments were on the original blog entry. After some technical difficulties, the blog had to be reconstructed, and this was the only way to keep the original comments.

Mike Clinebell

Dawson Great site

I have just two coments:

I appreciate your references to our company but "Clinebell" Is misspelled throughout this page.  Since ice is more prone to fracture at colder temps, it is much more crittical to temper our blocks, i.e., get the entire block up to 32 degrees before you start carving.  Our block comes out of the machine at about minus 18 degrees on the bottom and plus 32 degrees on the top.  Since "can" ice is only freezing, at most, 5 inches of ice from any point,  you don't deal with the extreme temp differences, thus the entire block will temper much quicker. Ice is a very good insulator and with this in mind it will take longer to "warm up" the middle of a block.

Thursday, March 22, 2007 - 09:37 AM

Dawson LIst

My apologies to Mike and his company for my poor spelling. It'll be a couple of days before I can fix the errors, because I've used up all my available space on the server, but I can comment right now. Apparently I've been misspelling Clinebell for a while, but I would occassionally spell it correctly. I need to try to add it to my spellcheck dictionary. But Mike brings up an excellent point as to why Clinebell blocks are delicate and prone to fracture when they come out of the machine: there is a 50 degree temperature differential from one side of the block to the other. No wonder they pop sometimes! Given this, I would argue that you should always try to keep the bag on the block after you harvest to give the cold side of the block some protection. I know that if I wasn't going to put a block in the freezer right away, I'd also put a sleeping bag over it to give me a little more insurance. Thanks Mike!

Friday, March 23, 2007 - 11:00 AM