For many years one of my spare time activities has been to locate old research microscopes and restore and modify them to make them not only "as good as new", but, if possible, better!

One interesting and challenging one was a Nikon S-Pol, a polarising microscope of the Nikon S family of microscopes made from the mid 1950s to the mid 1970s or so. The S microscopes can be described as high quality instruments with a single terrible flaw. The fine focus mechanism had a nylon gear that would slowly shrink as its crystallinity increased. Eventually it would split whether or not the instrument were used. This particular instrument also had some missing and damaged parts. Eventually I either found replacements for everything missing or faulty including, most recently, a brass replacement for the dread junk nylon gear!

A few days after completing the Nikon S-Pol project I was admiring the beautiful instrument whilst drinking a cup of espresso. It occurred to me that because espresso has substantial concentrations of caffeine, and because caffeine crystallises readily, perhaps caffeine crystals would appear if I put a drop of the espresso on a clean slide, along with a spot of crema and then let the spots dry. I did this, and let the slide sit until both had dried completely.

Before using examining the slide I attached a microscope camera to the instrument. I made images of what I saw.

When I put the slide on the stage of the old, but once again perfect condition instrument, with the polarising filters crossed so that the field of view was dark, there were bright crystals all over the dark field! Most of them were shaped like microscopic lemons!

Polarising microscopes have rotating stages. The plane of vibration (electric vector) is normally set so that it is along the 12:00-6:00 line, and the plane of polarisation is along the 9:00-3:00 line.

I slowly rotated the stage. As each Lemon shape became oriented to the 12:00 to 6:00 line it vanished. When it got to the 9:00 to 3:00 plane it again vanished.



Polarising microscopes normally have a slot for introducing special optical devices to retard light vibrating in different planes differently. When this is done with the usual quarter wave plates the background colour will shift to a magenta and the colour of birefringent crystals will change. In this case the little lemon crystals would appear to be blue or yellow. As the stage rotated, the crystals would change from blue to yellow or yellow to blue as they passed through the 12:00 to 6:00 plane, and again the 9:00 to 3:00 plane.



The crema was different. Under cross polarising filters there was material that was obviously crystalline, because it was visible. There were also a few of the lemon shaped crystals.



With the "quarter wave plate" installed this material look like this:



I am not absolutely certain the the compound that formed these crystals is caffeine--there are hundreds of components in coffee. However, caffeine crystallises very easily, and most of the other compounds are present in much smaller concentration. Most have more complex shapes that also tends to retard their crystallisation rates. (With most monitors the images will be magnified about 400 times.)

Robert,

No one else posts like this!

Since you have teased us with a description of that vintage microscope, could you show us some photos of it, please? (A bird and/or espresso machine in the photo will give a sense of scale.)

Very cool

Here is an image of the Nikon S-Pol microscope. The small gear to the lower left is the bad nylon one that was replaced. It is amazing how one badly made part can make a large instrument like this unuseable. The Micro Casa A Leva stock portafilter is sitting by it for scale.

So awesome! Thanks for sharing! The lemon shape added a bit of humor

Amazing thanks.

You could compare slides from regular and decaf coffees...

What a nice read to wake up to...

Thanks Robert!

You should post those up somewhere for download in high resolution. That would make a nice wallpaper on the computer especially on a 4K display.

I am currently working on the polarising microscope. A friend of mine is planning on visiting here in a few weeks. He has a very high resolution camera, we will probably try to get high resolution images when he is here.

Yes! Would love to use your photos as a background, or even put them on the wall.