There are a lot of ways that stresses can show up, at least when discussing materials science. Cracks in concrete are a common enough example, but any catastrophic failure in a material is often attributable to some stress that couldn’t be withstood. If you’re interested in viewing those stresses before they result in damage to the underlying material, take a look at this DIY polariscope which can view internal stresses in glass and other clear objects.
The polariscope takes its name from the fact that it uses polarized light to view the internal structure of a transparent object such as glass. When the polarized light passes through glass in a certain way, the stresses show up as lighter areas thanks to the stressed glass bending the light back into view. This one is constructed with a polarizing filter placed in front of an LCD screen set to display a completely white image. When glass is placed between the screen and the filter no light is seen through the polariscope unless there are stresses in the glass. Even placing a force on an otherwise un-stressed glass tube can show this effect, and [Advanced Tinkering], this project’s creator, has several other creations which show this effect in striking detail.
The effect can also be observed as colored areas in other plastic materials as well. It’s an interesting tool which can help anyone who frequently works with glass, but it’s also interesting on its own to see clues left behind from the manufacturing process of various household items. We’ve seen some other investigative methods for determining how other household items are mass produced as well, like this project which breaks down the injection molding process.
Continue reading “Stresses Revealed With A Polariscope”
According to [Kelsey], transparent displays are guaranteed to make “everything feel like the future.” Unfortunately they’re hard to find, and the ones typically available are OLED and can’t make solid black colors. But as luck would have it, it’s possible to repurpose a common LCD to be sort of transparent.
A LCD uses nematic crystals that can polarize light, with the amount of polarization changing based on the electric field applied to the crystal. Light enters the front of the panel through a polarizing film, passes through the display, and then bounces off a reflective back coating. The display itself usually polarizes light in a way that matches the front polarizer. That means if you do nothing you get reflected light. However, if a part of the LCD gets an electric field, it will repolarize in such a way as to block the reflected light making the display look black in that area.
[Kelsey’s] trick is to peel off the reflector and replace it with polarizing film taken from another display. The new polarizer needs to be bigger than the display for one reason: you need to match the polarizing angle of the front film with the new back film. That means if the new film is exactly the right size, it won’t be able to rotate without leaving gaps. By starting with a larger piece, you’ll be able to rotate for maximum transparency before you stick it on.
We’ve seen some homemade transparent numeric displays. The transparent wood, though, has usually left something to be desired.
Artist Pe Lang uses linear polarization filters to create an unusual effect in his piece polarization | nº 1. The piece consists of a large number of discs made from polarizing film that partially overlap each other at the edges. Motors turn these discs slowly, and in the process the overlapping portions go from clear to opaque black and back again.
The disc rotation speed may be low but the individual transitions occur quite abruptly. Seeing a large number of the individual discs transitioning in a chaotic pattern — but at a steady rate — is a strange visual effect. About 30 seconds into the video there is a close up, and you can see for yourself that the motors and discs are all moving at a constant rate. Even so, it’s hard to shake the feeling of that one is watching a time-lapse. See for yourself in the video, embedded below.
Continue reading “This Art Project’s Video Is Not A Time-Lapse”