by
Richard Haynes
Missouri, U.S.A.

A few days ago, in order to test my homemade polarizing filter system, I made a few quick slides of various crystals. Yeah, I know, I shouldn't just put a couple of water drops on a slide, add a bit of chemical to the water, stir, then place the slide under an infrared heat lamp to rapidly dry it. But I did. A press of other matters caused me to rush this little task. Even so, it turned out to be fun because I came back to it later and spent time with it. Why? Well, my cut-by-hand polarizing filters worked very well and I made a few photos that were reasonable. One of the chemicals I had pulled from my shelves for the test was potassium acetate. Not thinking everything through in my initial efforts, I had forgotten that this white crystalline powder is, as are many chemicals, a "little" hygroscopic, i.e., it picks up atmospheric water rather easily. And, fast drying the chemical solution under a heat lamp seems to speed up the process.

My first look at the potassium acetate slide under polarized light showed beautiful, regular rows of soft, fluffy crystals, almost like feathers on a bird. However, when I left the microscope for a few minutes and returned to see nothing but black (polarization extinction) no matter how I shifted the slide, I was puzzled.  Then, remembering a tad of basic chemistry, I removed the slide to find the water droplet. I had been looking through a (now) clear solution of potassium acetate. Duhh!  But, what I had seen prompted me to look again another day.

So, I spent sufficient time to make photomicrographs of polarized potassium acetate. I attempted to create a moment by moment look at the deliquescence (water pick up) phenomenon. It required some quick footwork between the heat lamp and the microscope followed by rapid microscope and camera settings (I have no hot stage) to get the slides to the stage and photographed.  After a number of failures, I developed a procedure that worked for me. The pictures below are my results at 40X.

                                       
                              Fig. 1   The first soft rows of crystals                                Fig. 2   Crystals look almost like an ice wall

                                      
                               Fig. 3   A different area of the "ice wall"                         Fig. 4  Black areas hint at solubilization

                                     
                                Fig. 5   The beauty of polarization                                  Fig. 6   30 seconds later black areas spread

Now, the deliquescence process has begun take over the slide.  Seconds after figure 6, we see major changes occurring.

                                      
                                 Fig. 7   Canyons are being carved                               Fig. 8   A slight slide shift reveals "badlands" 

From this point on, I was shifting the slide, checking the camera and snapping as quickly as possible. Deliquescence was taking over very rapidly. It was as though I was viewing the breakup of a continent.

                                      
                                 Fig. 9  Deep erosion                                                        Fig. 10  Small pieces are floating

The last two photos: deliquescence is in total control

                                       
                                 Fig. 11   A mass of swirling bits                                       Fig. 12  The last intact pieces on the slide

And after figure 12 photo was taken, there was left only a tiny pool of water on the slide. Deliquescence has triumphed.

For once, a mistake of mine (and there are many) seems in the end, to have turned out okay. Looking back, I'm glad I was in a hurry.


Equipment:    Nikon Eclipse E200 trinocular microscope with Qioptiq digital coupler and Nikon CP 4500 digital camera. Photoshop® 7.0

     

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