Across the Fence: Schlieren

If you have ever been dealing with glass, you might know this Germanism in the English language: Schlieren (pronounce: ‘shlee-ran, meaning streaking). Interestingly, the English language only knows of the Germanism as of an inconsistency in a transparent material, so-called inhomogeneities. A Schliere in a glass breaks the light in a different way. There is an entire field in science dedicated to the ways Schlieren do this, in order either to create lenses without Schlieren or to create specific visual effects. Apparently the so-called Schlieren effect is used in video projectors – thus, Wikipedia.

Let me tell you, that Schlieren usually mean to me another kind of effect on glass (not IN glass). When you are cleaning windows, you will realize that there are Schlieren where the glass is not yet clean – either because you haven’t done enough cleaning, yet, or because your rag is rather distributing than taking off the dirt. I used to love to clean my German windows; I didn’t even mind sunshine because, then, I would see where there were still Schlieren. American windows are no fun to clean, at all. It also happened back in the day when you took glasses from your dishwasher – though I presume that had a different reason, because the Schlieren wouldn’t come off of some glasses, wash and polish as you might.

Schlieren also form when an oily liquid meets water. Any kind of movement by wind, waves, or disturbing with a tool creates the rainbow-colored effect. Unfortunately, we see this more than often – think of puddles at gas station after a rain shower, of lakes or rivers, anywhere gas or other fats contaminate water. It’s fascinating that we perceive the disturbing fact as an iridescent film on top of the waterbody. The beauty of the nasty.

The term Schliere signifies even more phenomena in the German language. Such as striped zones within an otherwise homogenic rock. It can be the different density of gases in our air mixture, leading to what we know as the heat shimmer above a landscape. Check minute 1:28 in this video, and you will know what I’m talking of:

Or we perceive Schlieren when we have a defect in our retina – certainly not anything I hope you have any experience with.

Basically, the artful mixture of paint on water such as in the Japanese technique of Suminagashi is the prerogative for decorating cloth or paper:

The inks contain oil and, therefore, swim on top of the water. The Schlieren create sort of a print effect. I’ve tried it back in the day as a journalist for a trade magazine. It was fun, the results were beautiful. I still wonder what they did with the water afterwards. I guess, I’m getting more pensive the more I reflect …

Caption
Even when there is little of either, oil or water, the Schlieren can be very distinct on impermeable ground. (Photo: John Rourke @https://unsplash.com/)