An 1842 Photo Technique Still Has Its Charms

Decades ago, when my brother was first hired out of graduate school, one of their Swiss clients was kind enough to send him a hands-on science-gift every Christmas. And my sibling was in turn generous enough to give them to me. When he no  longer worked for the company that was linked to that benefactor, I wrote to the Swiss Santa, explaining how my students had benefited from the educational experience made possible by their offbeat, well-thought-out gifts. They happily obliged, and until the financial crisis of 2008, every December, they continued to send us science-related kits and toys .

One of my favorites was a cyanotype kit. Cyanotype can be used as a printing process, but it’s also one of the oldest photography techniques, dating back to the 1840s. Through serendipity, the astronomer John Herschel first created the necessary emulsion of ammonium iron (III) citrate and potassium ferricyanide, which supply the ions needed to produce a beautiful blue precipitate. Before it can be used, the emulsion has to absorbed onto paper or cloth and then allowed to to dry in the absence of sunlight or any other source of ultraviolet.

Recently I dug out some cyanotype paper from the Swiss kit to review the chemistry involved and to witness another happy marriage of art and science. If the paper wasn’t over 10 years old and not slightly oxidized or affected by humidity, it would look greenish, the color of ammonium iron (III) citrate. But mine was a very pale blue. Yet because the changes are reversible, the paper still turned out to be functional.

In the upper left photo, the compass has been sitting on the emulsion paper for about 3 minutes and the original light bluish color is fading. The paper has gone almost completely grey after 8 minutes of exposure, as seen in the photo in the upper-right-hand corner. Indoors, I removed the compass and the parts not exposed to light are now light blue (picture at 3 o clock position). But when placed in water for about 2 to three minutes, the bit of blue disappears (not shown). Finally as seen in the final photo, a deep blue appears in areas that were exposed to UV.

How do we account for all the color changes?

Pictures 1 and 2

When ultraviolet strikes ammonium iron (III) citrate, (oxalates are also used and preserve better) the citrate converts to acetone dicarboxylic acid by donating an electron to the ferric ion Fe3+, reducing it to the ferrous ion, Fe2+. The Fe2+ in turn reacts with potassium ferricyanide( K3[FeIII(CN)6] · 3H2O) to create Prussian blue (containing ferric ferrocyanide FeIII [FeII(CN)6]+. But in bright sunlight, the reaction does not stop there. Instead the Prussian blue is converted into Berlin white (ferrous ferrocyanide = FeII2[FeII(CN)6] ).

Old nomenclature persists, and it sometimes turns off the uninitiated. Ferric ions and ferric-complexes contain the oxidized state of iron, Fe+3. Ferrous ions and ferro-complexes have Fe+2. The chemical properties of the different oxidation states differ more significantly than the slight changes in the suffix might suggest.

Picture 3

Initially the only light-bluish parts are the ones that still have the compounds of the original solution, the parts that did not get exposed to ultraviolet light. Notice that because the sun was hitting the compass circle at an angle, it cast a shadow, and that shadow is light blue at this stage.

Unshown Picture

The reason that the light blue (or green if you have fresh paper) disappears is that the original soluble emulsion is dissolved away in the water.

Picture 4

As the paper dries and gets exposed to oxygen in the air, the Fe2+ that is in the grey compound(outside of the cyano-complex) of the light-exposed areas is oxidized back to Fe3+.  Prussian blue is generated. It’s the same blue end-product of the invisible ink trick that was part of children’s old chemistry sets. Peak absorption of light in the 690 nm region of the spectrum is used to move an electron from Prussian blue’s Fe2+, part of the cyano-complex, to Fe3+ ions , resulting in us perceiving a deep blue.

To use it as a printing technique, instead of placing an object on the emulsion paper, you can either draw on an acetate and then proceed as usual. Or you can print a black and white photo on a transparency and place it on the paper to create a cyanotype or a “blueprint”,  as old architects would say. Here are my blueprints of both suggestions, some loves of my life outside of science: trees and my wife.


The Swiss Santa’s Cyanotype Kit Bioengineering

Chemistry and Light

Prussian Blue: Artists’ Pigment and Chemists’ Sponge

Mike Ware Buxton, Derbyshire, United Kingdom. J. Chem. Educ., 2008, 85 (5), p 612

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Icicle Adventures

Despite below freezing temperatures, ice can melt in sunlight. This indicates that ice molecules can easily get agitated to above freezing temperatures even if surrounding air molecules have less energy of motion. If the melt-water runs down an edge, heat can be taken away again from the dripping water. An icicle begins to form. If water keeps flowing over the bud, the icicle will grow. It not only serves as a continuous source of crystals, dripping water helps take heat away from the growing icicle.

When ice forms, it actually releases heat. What, aside from water, takes heat away so that more flowing water can freeze?   It is the up-draft of air caused by the icicle being  warmer than its surroundings. The heat is taken away more slowly at the top of the icicle, where it grows more slowly. At the base, the opposite is true; growth is faster, hence the carrot shape.

With all that mind and the expectation of seeing the same pattern again, I was of course startled when I saw this yesterday:EQlXZbGWkAIaTCz

By looking around, I soon realised that’s not what the icicle looked like when it formed. A meter to the left of that strange upside down V-formation, I noticed the following.


In all likelihood, the odd shape originally had three components, a familiar carrot shape but joined to a pair of other icicles that had grown along the edges of the angular frame. Metal is efficient at removing heat, and it probably adds a complicating variable to the shape of the arms clinging to the metal. One of the arms detached itself from the frame upon partially melting and then rotated; the other arm broke off.

I was tweeting these two pictures when I told myself I should be out there instead, observing to verify if guess was right. The same structure to the left now looked like this:


Seconds after I snapped the photo, the whole structure came crashing on the floor of the deck. It never got a chance to rotate as much as the original icicle.

The best, however, was yet to come. Annie van Leur saw my pictures and remarked the following:




Cute. However, not as interesting as our Michigan ice apples. When freezing rain coats rotting apples and the mushy rotten apple falls out, it leaves a shell of ice.

And she posted this:


Why are there often ridges on icicles? It’s ionic impurities in the water that play an important role. Graduate student Antony Chen designed a table-top apparatus for the controlled growth of icicles. He experimented with different conditions of temperature, water supply rate, ambient air motion, and water purity. When pure water was used, ripples did not appear on icicles. They looked like the icicle in Figure 1. Even a low salt concentration (0.008%) caused ripples to grow and travel on icicles (Figure 2). In the absence of salt,  dissolved gases or non ionic surfactants had no effect on the growth of ripples. When the air was still, icicles grew more tips (Figure 3). Gently stirring the air caused the shapes to become more monotonous.

Figure 1
Figure 2
Figure 3




The Point of Icicles

Experiments on the Growth and Form of Icicles

Icicle Photos







Economics Vs. Environment: A False Dichotomy

mid-globeThe false dichotomy of economics versus environment has long existed because it is unfortunately too easy to sweep health and environmental costs under the rug or to have government consistently pick up the bill for consequences of short-sighted “growth”.

Here’s a letter sent to the Economist by former World Bank, senior vice president, Vinod Thomas, specifically arguing that by addressing climate change we are really safeguarding the economy in the long run.

It is true that climate change is not just an environmental problem; it cuts across all activities. Yet the recipe for economic growth from mainstream economists, including those of the The Economist newspaper, disregards climate change.  Yes economic textbooks cover externalities or spillover effects, but these have not been integral to growth analysis. A search finds abundant climate studies, but less than 0.5% of the numerous growth articles over the past 50 years seem to factor climate effects.

That allows politicians such as Jair Bolsonaro, Brazil’s president, to argue that environmental protection is inimical to growth,even as the emerging reality is the opposite. American policy too, sees any deregulation, including policy that mortgages the environment, as pro growth. Yes environmental destruction may boost short term growth, but the climate outcomes hurt long term growth and welfare.

So changing the conduct of growth economics is essential if we are to avert a climate catastrophe.Unless the economics profession stops ranking and rewarding countries based primarily on how much they deregulate and boost short term GDP, the climate action that you rightly call for will continue to lag dangerously.

Here is another discussion from the journal Nature that is more detailed and broader in scope:

The cost of a warming climate


Storks and the Biological Facts of Life

Many years ago, I got into the good habit of keeping a journal while my kids were growing up. Here’s one of my favorite entries. 

My daughter, who is in the first grade, went to an art museum with her class today. She told her Mom that lots of statues were showing their private parts. In the morning she had also showered with her mother, so not surprisingly, my daughter came out of it saying she wants breasts.

284613678011211Kids, of course, occasionally think of precocious thoughts that simply float away. But I cannot help contrast her childhood to mine. I never showered with the parent of my own sex; in fact, luckily, I have yet to see my parents naked. When my mother was pregnant with my brother, I was my daughter’s age, and I had seen a picture of a stork that held, from its beak, a sling with a baby. There were fluffy clouds in the background, and that’s where my brother was coming from—the sky.

One day, our tenant’s daughter, Manon, claimed that my baby brother was in my mother’s belly. I remember exactly what crack of the sidewalk I was about to step on when she said that. Manon had made the world stop. I recall looking across the street at the front entrance, expecting my mother to magically open the door and promptly deny the absurdity. It was like being told that the milk came out of the milkman’s ear.

Luckily, later that evening, after laughing and realizing that I was not ready for the truth, my mother assured me that a stork would indeed bring the baby home. Astonishingly, even though I know from recent accounts that my mother had apparently remained relatively thin throughout the pregnancy, I had never noticed her belly. My brother was not exactly born hamster-sized, so I must have never looked below her face.

Five years later in the sixth grade, my friend, whose first name was the same as mine, came to school with a shocking piece of news. As we walked past the nun’s residence, he quoted a World Book Encyclopaedia article on reproduction. It claimed the process started when a male part of the anatomy was placed in the female counterpart. How could that lead to a baby? Could unscrewing the back of a TV and sticking a prosciutto ( ham) into it create a cooking show? But half the boys in our class seemed to confirm what was in print, and the encyclopaedia had never lied to me. I wrestled with the idea for a week, considering the possibility that a secret had been kept from me. But accepting the idea became more difficult when the same friend had concluded that this was only one way of reproducing. Surely, our parents had used some other means.

A few weeks ago my daughter, who has a fascination with bones, was looking at some anatomy drawings in one of our medical books. She turned the pages and came across a diagram of a scrotum and asked what it was for. It produces seed needed to make a baby, I told her. “That’s how babies are made?” she asked, grimacing. I realized that I had told her too much.

Our children need their childhood.

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