You can make a lens out of ice, at least in theory. I read that long ago, and only recently again encountered the book where I had read that. Max Planck’s book, The Theory of Heat Radiation, which is available in an inexpensive reprint. Right up front, in the second paragraph: “Radiation of heat is in itself entirely independent of the temperature of the medium though which it passes. It is possible, for instance, to concentrate the solar rays at a focus by passing them through a converging lens of ice, the latter remaining at a constant temperature of zero degrees, and so to ignite an inflammable body.”

About a year ago, I experimented with making an ice lens. A shallow bowl of water placed in the freezer will become a half-lens (plano-convex), and two of those could be “welded” together to make a lens with two convex surfaces. The welding being done by warming the surfaces to be attached, to have a thin layer of water on the ice, and putting them together until they re-freeze. Just like the welding of metals, actually — only at moderate temperatures. Such a lens would not be ideal, but it should be sufficient for experimenting with focus.

However, that simple method did not work. There were lots of bubbles in the ice, making it cloudy. Also there were cracks, fractures. The ice near the boundary of the lens tended to be fairly clear, maybe 1 cm depth, but the interior was cloudy. One might experiment with the welding together of small clear portions of ice — that would probably work, though it would be tedious.

Boiling the water, before freezing it, helped drive out air dissolved into the water. That produced a lens which had only about one-third of its area obscured by cloudiness. Think of an ice lens with a cataract. With two-thirds of the lens being clear, it should be possible to do the portion of the experiment which involves focusing the rays of the sun.

I did not carry those experiments through to completion. Suffice it that the process of making a ice lens has some subtleties. However, Planck is correct — if one makes an ice lens, I’m confident it would be able to focus the sun’s rays, while itself not melting.

Now, there is a flip side to that observation: Think about means of possibly removing the cloudiness from a lens which has already been frozen. Clear water contains dissolved air, and we can see through it. But when the water is cooled, air comes out of solution. The water molecules (H2O, polar) are attracted to one another more strongly than they are attracted to the air molecules (99 percent N2 and O2 modlecules), and the freezing water “pulls away” from the air molecules, leaving tiny bubbles of air. That is what produces the cloudiness, I believe. (This is all hypothetical on my part, and I’m sure it would be interesting and informative to do further trials of these points. A meaningful science fair project topic, in my opinion.)

Now, there are (at least) two ways to deal with the air bubble problem. (1) Remove air beforehand, by boiling. Or perhaps by some fractionation process — eg, freezing, separating the clear ice from cloudy ice, discarding cloudy to keep only the clear ice, remelting the clear, and refreezing. Repeat perhaps. That might refine the ice to have very little dissolved air, hence be clear. Or method (2) Melt the air bubbles further, or rather melt the ice near them, so that they combine and become fewer bigger bubbles. That is a sort of annealing of the ice. I’ve not run any experiments along that line. But I wonder…

If light will not travel through the cloudy parts of the ice, then it must be heating the ice there. So what if we put a cloudy ice lens (or any other lens, lets say glass) under an intense light. Do its bubble areas melt, coallesce, and refreeze with larger bubbles, thereby reducing the overall cloudiness? In essence, we are creating a context in which the undesirable cloudy areas are incentivized (by heat) to transition to a less cloudy state. That is what I meant by the flip side of Planck’s observation. In general, the flip side of most scientific ideas gives one an interesting technique for transformation, measurement or other interaction with natural materials. One of my favourite sayings is from an old movie, detective Charlie Chan, who says “No experiment is a failure until the last experiment is a success.” In other words, we can learn as much (perhaps more) from our negative experiments as from those which have expected outcomes.

Actually, such selective heating of ice to clear cloudiness may occur in nature. What happens if slabs of ice are left outside, under the sun’s rays? How does the cloudiness clear? What about mechanical flexing of the ice? Think of “black ice” on the highways, which has been driven over many times by cars — how does white ice become transparent, hence black on the roadway?

I’ll leave these ideas about ice experiments with you, for your enjoyment. My personal interest at the moment is reading further in Planck’s book. More on other Planck-related topics in other posts.

Best wishes,
Ken Roberts
16-Apr-2014