Icicles between crossed polarizers

[Andy Perrin]

A long time ago I read something about the birefringence of ice crystals. Birefringence is a when a material has different refractive index in different directions, causing a ray of light to split into two rays, one called the "ordinary ray" which keeps going in the direction of the original light, and another called the "extraordinary ray," which can be at a different angle, depending on how the light hits the crystal. The two rays vibrate in perpendicular directions, or polarizations, and they move at different speeds. As a result, one ray can get delayed with respect to the other and interfere with it. When the crystal is placed between crossed polarizers, the interference makes lovely colors. 

 

In the last few weeks I noticed some giant icicles forming on the building next door to me, and bearing in mind what I knew about the birefringence, I decided to snap some icicles off and photograph them on a light table between some plastic polarizing sheets and a circular polarizer on my camera lens. I harvested the icicles during the daytime and stored them in my freezer. Then after work, I photographed them. 

 

For the camera, I used my brand new (to me - it's used) A7iii, which is unconverted at the moment. I put a Tiffen circular polarizer on the lens of my Nikon Micro-NIKKOR 55mm 1:2.8, which was mounted on my copy stand. I used an A4-sized polarizing sheet on my light table, hooked the camera to the computer with the focus approximately set, and got the icicle out of the freezer. I then fine-tuned the focus as fast as I could, and shot a lot of images at different exposures to bracket with. Then I tossed the icicle out the window, one second before I realized that I'd forgotten to take any NORMAL photos of it for comparison. Oopsie.

 

 

Because birefringence depends on the angle, you get different colors when the object is at different angles.

 

Here's a crop of a pretty part:

 

Kind of opal-like!

 

The colors have been pushed a bit in the above photos, because obviously seeing them is the whole point here.

----

 

Having photographed an entire icicle, the next day I started to think, "but wait, have I seen everything there is to see here? What about cross-sections?" Because icicles form layer by layer, so in principle you would expect them to have rings, like trees do. So out I went again to harvest another icicle. I got a huge one and stuck it in my freezer. Later that evening, I started to think about how to cut it into sections.

 

My first thought was to try to cut it with a heated wire. I rigged one up, and indeed the wire sank nicely into my test ice cube, but the ice cube REFROZE behind the wire, as it went through! So that idea was discarded. My next try was cutting an ice cube with a sharp kitchen knife. The knife hardly sank in at all. Then I tried sawing it with a butter knife, and that worked a little. The serrated edge was the key ingredient, pulling ice out of the groove. Once I had that realization, I got a bandsaw and that turned out to be the way forward. The other thing I discovered is that the best way to hold an icicle is with a potholder, because towels and paper towels stick to the ice and leave behind ugly loose threads or fibers. 

 

 

I started cutting from the small end (bottom tip) of the icicle (opposite from the end shown above, which is the base).

 

 

 

As expected, rings are clearly visible. I had been hoping the rings would be bright and colorful, but that's not what happened.

 

I tried another cut a little higher up the icicle.

 

 

 

This was more colorful, and the ice was getting clearer and less cloudy. 

 

Finally I tried a cut from the base of the icicle, which was very clear an glassy.

 

 

This one produced extremely bright colors with no "pushing" at all. Aside from cleaning up dust and hairs that got on the ice, and adjusting the black level to make the background dark, this is mostly unmodified.

 

The details here are fantastic.

 

1:1 crop:

[Nate]

Those shots turned out great Andy. I've used a CPL on lens photographing a subject in front of my computer screen that's completely white, the subject becomes back illuminated, but the background is black/seriously darker. Creates cool effects.

[colinbm]

Fantastic experiments & great results.
Yes the last couple are mind blowing.

[ulf]

Interesting that there are polarising stress in ice too.

That is a common method to observe stress in injection moulded parts.

It is/was used frequently for quick checking for optical media production for  production machine adjustments

[Wayne Harridge]

A great experiment with impressive results.  I've tried this with various clear plastic objects with good results.

 

This brings up another interesting situation with polarisers.  I recently purchased a variable ND filter meant to vary exposure by ~-1 stop to ~-10 stops, this works perfectly well on a visible only camera, but I tried it on my IR modified body and it only makes ~2 stops difference in exposure from min to max.  I did not really expect this but I guess the polarising material in this device is designed only for visible.  As yet I haven't tried this at the UV end of the spectrum.

   

[JMC]

Nicely done Andy, really nice photos.

[ulf]

@Wayne HarridgeNormal polarisers lose their blocking as you found out at the end of the VIS range, gradually getting less extinction.

I think I made a measurement that I posted of that here, but cannot find it now.

A long time ago , last century, Polaroid had a special polarisation sheets that worked further up into IR.

There exist scientific polarisers that work, but they are quite expensive and I do not think they are made in big diameters suited for many photographic lenses.

[Cadmium]

Andy, Fantastic! 

[Stefano]

Some topics on IR and UV polarizers:

 

https://www.ultravioletphotography.com/content/index.php?/topic/3652-near-infrared-polarizer-has-arrived

 

https://www.ultravioletphotography.com/content/index.php?/topic/3744-polarizer-in-uv-test

 

https://www.ultravioletphotography.com/content/index.php?/topic/3170-uva-and-uvb-polariser-moxtek-uvd260a

 

(these links link to posts and not the entire topics, I will try to fix that)

 

Also, it's quite off-topic, but some Mandelbrot-style fractals show similar patterns when colored using the orbit trap technique: https://youtu.be/GiAj9WW1OfQ

 

(Go to 7:00 for example).

 

[Andy Perrin]

10 hours ago, Nate said:

Those shots turned out great Andy. I've used a CPL on lens photographing a subject in front of my computer screen that's completely white, the subject becomes back illuminated, but the background is black/seriously darker. Creates cool effects.

Yes, the LCD screens are polarized so this is exactly the same effect. I recommend using a light table with polarizer sheet though because the monitor will show the individual pixels potentially if the pic is sharp enough and may make moire patterns. 

[Andy Perrin]

5 hours ago, Wayne Harridge said:

A great experiment with impressive results.  I've tried this with various clear plastic objects with good results.

 

This brings up another interesting situation with polarisers.  I recently purchased a variable ND filter meant to vary exposure by ~-1 stop to ~-10 stops, this works perfectly well on a visible only camera, but I tried it on my IR modified body and it only makes ~2 stops difference in exposure from min to max.  I did not really expect this but I guess the polarising material in this device is designed only for visible.  As yet I haven't tried this at the UV end of the spectrum.

   

Yeah, as was said above, normal polarizers don’t work out of spectrum. I own an IR polarizer that I bought on eBay (see Stefano’s link above!) for $50 or so, so keep your eye out and you might find a bargain. 

[Nate]

1 hour ago, Andy Perrin said:

I recommend using a light table with polarizer sheet

Thanks, great idea

[Doug A]

Fabulous photos with amazing colors. I've photographed birefringence in plastic, never realized it happens in ice. Fascinating. 

 

Thanks for sharing,

Doug A

[nfoto]

Indeed ice is full of "hidden" colours. Perhaps time to dig out some old files from the archives.

[Andrea B.]

This totally rocks, Andy !!!!

 

It appears as though some insect was trapped in the ice. Can that be so?

Perhaps dead insect on roof gets washed into icicle formation.

Or.....I'm reading things into an unusual pattern in the ice. 

 

This is like the icicle version of insect-in-amber only it isn't thousands of years old.

[Andy Perrin]

Thanks for the kind words!

Quote

It appears as though some insect was trapped in the ice. Can that be so?

Hah, you're seeing things, Andrea. No insects are inside the ice. Without the polarizers, it's quite transparent, and very obvious in real life that there was nothing there but water and air bubbles.

[Andrea B.]

(.....laughing......)

 

but LOOK here, Andy. you can see the winged insect quite clearly!! I "enhanced" the legs. you can't miss 'em.

(this is too funny.....!!!)

 

 

 

 

 

[Andrea B.]

P.S.  Joking aside....

A couple of these photos would make beautiful prints. Do you ever get prints of any of your work? I sometimes upload a file to the Adorama printing service. Not expensive and they do a good job for a basic glossy print.

[Andy Perrin]

I've only ever made prints using Fracture, for my mom. Good to know about Adorama.

 

Re the "insect": HAH.

[Andy Perrin]

Here's another slice 'o the icicle (...slicicle???).

 

 

[Andy Perrin]

[Cadmium]

I was seeing the same thing Andrea was, a bug frozen in ice, but examining the same area on the visual photo of the slice I see some similar lines but not much more.

But once you start seeing the bug, it is hard to get it out of your head.

 

[dabateman]

Yes I saw the fly in the 1:1 as well. But nothing is there in visible. 

Great image Andy. That section is worth printing. For that I have been using Smugmug printers.