Mystery Photo: Relief in the Hoar Frost


What a Relief!

We see a lot of hoar frost this time of year. Think frozen dew. The crystals can be quite spectacular.
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This morning I got up to the top of the butcher shop construction site and was inspecting my heavily frosted work from last night when I saw something very odd. The hoar frost was in a relief pattern spelling out words!

This was in an area where I had written on the white PVC pipe with a green Sharpie marker. Something interesting had happened. Some thinking about physics revealed why the frost was thicker where I had written… Can you come up with the explanation for what caused this?

Don’t look at the comments yet. Think about it. Subscribe to this post’s comments by checking the subscribe box and leave your idea in comments. After some people have left ideas I’ll give my ideas. It’s a fun little application of physics and leads to thoughts on how to save energy, something I’ll explain later. Don’t be shy!

Outdoors: 44°F/17°F Sunny
Tiny Cottage: 60°F/57°F

Daily Spark: The real question is should we kill Schrödinger’s cat.

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About Walter Jeffries

Tinker, Tailor…

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14 Responses to Mystery Photo: Relief in the Hoar Frost

  1. Cary says:

    It’s more chemistry than physics. Most crystals form from seed crystals. Something in the chemistry of the Sharpie was causing seed crystals to form encouraging the growth of crystals. My guess would be solvents in the ink caused the crystals to form. I’d assume older writing didn’t form the dense crystals since the solvents would have had time to evaporate just the fresh writing caused the crystals. Like I say chemistry not physics. Temperature changes caused by the Sharpie ink could also cause the crystals to form but my bet is it’s due to the writing being fresh. In cold temperatures it could take days for the solvents to all evaporate.

    • Hmm… That is a great idea but in this case I don’t think that is the cause, or not the whole cause. That particular writing was inked on 24 hours earlier and had been exposed to the hot sun all day. Other writing that I had put on with the same marker two days before showed the same results. Another sample that was only 12 hours old also showed the same results. I suspect that any solvents in the ink had long since evaporated. It is possible that the ink itself acted as you suggest but… SPOILER ALERT: STOP READING IF YOU ARE STILL THINKING OF THE ANSWER BECAUSE WHAT I”M ABOUT TO SAY IS A CLUE I had examined other inked areas and they showed different levels of relief. The height of the crystals varied with the color of the ink. Note that the background color was the white PVC in all cases. It is also possible that the result is a combination of your suggestion of seed crystals and what I’m thinking of as both of them could work together in an additive effect.

      • Bill Harshaw says:

        Rats–missed the time element completely.

      • Cary says:

        I take it the spoiler was temperature difference. The ink being darker would have more evaporation. The difference would be slight but possibly enough to cause the effect. Logic would indicate that the writing should have less build up so it is bizarre. It’s why I thought crystal seeding could be the factor but the time differences make that unlikely. Cold could slow a process of hours to days but it would be a long shot. Intriguing no matter what.

  2. Bill Harshaw says:

    I’d guess the pipe got cold faster where the marker ink was, accounting for the disparity. If the ink has alcohol, it evaporates fast and that would cool the pipe.

    I don’t see how it leads to energy saving though.

    • Excellent idea. Evaporative cooling is a technique that works very effectively. I have read that in some dry climates they use what are termed Swamp Coolers or evaporative coolers. I am not sure if that would be effective in our cold climate using water but some liquids like alcohol would work. Might make for a vodka air conditioner! But, as you noted in your second comment, the time element means that isn’t the answer here.

  3. David lloyd Sutton says:

    I suspect the solar load left the sharpied markings marginally hottter, going into the period of frost deposit. Looks like the green lines are more translucent, and possibly a tad higher, which would accord with melting and clear ice deposition in those areas as opposed to more “fluffy” deposts on the unmarked areas.

    Here in Davis we are in the sixties daytime and forties at night, about 75% humidity, which makes for chilliness morning and evening. Everything is greening up on the ground after our first rainy weeks, and the deciduous trees are magnificent in red and gold. Of course we also have everything from pines to oleanders to rosemary staying green, so we have variety.

    • I don’t think the solar load is the issue since it was dim and then dark long before the frosts started forming. We lose our sun before 3 pm these days due to Bear Ridge to the west and simply that it is approaching the Winter Solstice. But, you’re close to what I think is the answer, in a backward, darkish sort of way…

  4. Spoiler Alert! Don’t read further if you haven’t formulated an solution and still want to try one on. It is never to late to post ideas to these thinking problems! While the crystal seeding may well have something to do with it I suspect, strongly, that there is another effect going on here. Think of Luke in Star Wars being urged to go over to the Dark Side, or not. There is something called black body radiation that relates to what may well be going on here. Essentially darker surfaces radiate better which would in turn cause more rapid cooling and thus faster crystal growth. The effect is small but enough over the course of the night that come morning when the first rays of the new day’s sun hit the pipe the greater depth of the crystals where the writing was shows a shadow of relief in the photo above. This black body cooling if I might call it that is the opposite, perhaps we should say the corollary, of why dark tar parking lots heat up so well, why darker vehicles soak up more light and why solar collectors are painted black instead of white. Follow this thought chain to my lunar panels, a.k.a. Dark Panels, which I’ve mentioned several times before. By using matt black dark panels we can get a little more efficiency in the radiation of the slaughterhouse’s carcass heat out to the dark night sky. By doing this we reduce our reefer’s cooling load. Furthermore, by placing the dark panels high above the rooms they serve we are able to use a passive thermo-siphon loop to dump heat to the sky without using any electricity at all. Electricity saved is money in my pocket and a reduced carbon load on the planet. All good things. And there is the answer to Bill’s puzzled question of how this could save energy.

    Further Reading:
    Black Body Radiation
    The Zeroth Law of Thermodynamics
    Crookes Radiometer
    Leslie’s Cube

  5. Edward says:

    I must say I really love your mystery photo sessions. I don’t generally get the answer right and am hesitant to leave a guess but I love reading both your and the answers of other readers solving the problem. I learn a lot. You are sort of like a cross between the mythbusters and that science guy. Keep on teaching!!

  6. David lloyd Sutton says:

    Ggrnghh . . .

  7. Nance says:

    what Edward said! lol Do enjoy reading all your posts.

  8. Eric Hagen says:

    This post is old, but a break from studying would be nice. I was thinking it had to do with the differences in albido. The darker ink soaks up more heat and PVC doesn’t conduct heat well, so their is still a good heat differential by the time the hoarfrost started forming. I would’ve guessed it would’ve been embossed though. Cold air can’t hold as much moisture, which is what causes frost and dew, but I always think of condensation as collecting on cold things, like a cold glass of water in the summer. Warmer relatively saturated air on a cold substrate. This would make me think that the white PVC would frost more. Perhaps the darker ink melted the surrounding frost causing water droplets to collect where the hoarfrost wasn’t, on the ink. In time when the inked areas cooled down enough the collected droplets froze and ended up having greater volume than the surrounding white areas. Hm, I’m interested to read the comments. I like how the color glows through – little natural fiberoptics.

  9. Eric Hagen says:

    Oh! Blackbody radiation, I forgot about that!

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