Inside an Ice Cube

Photo of the week #6: My potw is a bit of a cheat this week. I'm currently transitioning between jobs and am having a very hectic week trying to wrap up my work here at MUN. So, rather than try to find the time to take a new photo, I'm posting a few that I shot here in the lab over the last few years. I've been meaning to post them for a while now anyway, so now seemed like as good a time as any!

Part of my work here at MUN has been to perform laboratory tests on ice in the coldroom at the NRC-IOT. The tests focus on trying to figure out why ice breaks the way that it does. Once the tests are over, I've often 'thin-sectioned' the ice to gain more information about its physical structure. In the case of ice, this means attaching a sample of ice to a glass slide, then using a microtome (basically a sharp blade) to shave the ice down to a very thin section. When you look at the section between crossed-polarized filters, the different grains that make up the ice show up as different colors depending on how the crystal structure of that particular grain is oriented. It's a very beautiful effect - the colors in these photos are actually true to life.

This first section was taken while I was testing out the microtome at the start of a test series. In order to make sure that the equipment was working properly, I let a paper cup full of water freeze, then sectioned it. This photo shows how the grain structure of the ice looks if you are looking down at the top of the cup. The black circles in the photo are air bubbles, which get pushed to the center of the ice as it freezes (like in an ice cube). They form because the ice starts to freeze from the top, bottom and sides all at the same time, which pushes the air to the center of the cup:

This photo shows the same frozen cup full of water, but this time sectioned along the height of the cup:

For interest sake (and because I like them!), I'm also including a few shots of sections that I did using other types of ice. This one shows lab grown ice that I made using ~ 4 mm seed ice:


This one shows what hard-packed snow looks like when sectioned (very small grains because it's formed from snowflakes!):


This is an example of iceberg ice. Iceberg ice is interesting because it's structure can vary greatly depending on the particular iceberg. That means that the grain size and shape are often very irregular and you can often see big cracks (like the ones in this photo):


And finally, this is a shot me in the coldroom taken by a former workterm student. In this photo I'm using the bandsaw to rough cut ice samples for testing. It's usually -18 degrees celcius in this cold room plus windchill - burr! This picture was taken when the defrost cycle was on. The cloudiness in the picture is the moisture in the air - the coldroom is humidity controlled so when the ice melts from the refrigeration system during defrost, it ends up suspended in the air. You can actually taste the moisture!