Polarized light microscopy
If polarizers were not used in mobile phones, getting them would be a heavy task. Fortunately, polarizing films for phones are accessible and even decent.
Phone polarizers are sold with protective films on both sides. They spoil polarization properties and preclude their estimating in the way of assessment the strongest light extinction, turning the polarizer in a shop into a pig in a poke. Moreover, one side of the polarizer is covered with glue. The glue can be removed with the help of strong alcohol. It doesn't dissolve, but becomes soft and can be peeled out (even in one piece, if you are careful enough). Acetone-based solvents help to get rid of the glue too, but they help to get rid of the polarizer as well.
The direction of transmission can be determined from position of the strongest light extinction, if you have two identical polarizers, and values of transmittance can be derived from raw photos of the polarizers in transmitted light. Measuring of transmittance values of 1 layer and 2 layers with parallel directions allow to calculate transmittance values of 1 layer along both highlighted directions.
Polarizing film for iPhone from a radio market. The sellers provide no parameters, but significant ones can be measured at home.
Removing of the glue after alcohol treatment
The listed values mean that the transmission in the wrong direction can be easily eradicated: if one layer of polarizer has transmittance [0.9 0.01], two parallel layers have [0.81 0.0001]. Polarized light microscopy needs one polarizer ("polarizer") between light source and the object, and the second one ("analyzer") between the object and objective lens. It's better to make the "polarizer" of 2 layers (to diminish undesirable transmittance) and "analyzer" of 1 layer (to diminish worsening of the image). In this case, crossed phone polarizers nicely block even bright light: illumination of the field of view is noticeable, but insignificant.
Since transmittance depends on color, using of polarizer requires white balance correction. Values derived from the previous table (for Sony NEX-5 raw colors; mean value is normalized to 1):
For convenient use, the polarizers should be installed into a simple rotating device attached to the microscope stage.
Photos
The photos were made with Sony NEX-5 camera attached to Biolam S-11 (Биолам С-11) microscope. The images with white background are taken without analyzer (≈ in usual light), and the other ones show the same objects between crossed polarizer and analyzer. Two sticks in the circle indicate direction of transmission (thick one for polarizer, thin one for analyzer). For some objects, synthetic images of maximal and minimal brightness are given (the object is imaged at several/many angles of rotation of polarizer+analyzer pair and then each pixel is filled with its maximal or minimal brightness).
The field of view is 3.9 mm in diameter in most cases (otherwise a scalebar is embedded).
Videos of some of these specimens during rotation of polarizer+analyzer pair:
More crystals of citric acid.
Some specimens contain an admixture of methylene blue.
Water ice (0.94 mm thick).
Eggshell of domestic chicken (0.02-0.03 mm thick section)
Sand from Dnieper river in Kyiv (0.16 mm thick section)
Chicken from a shop, cartilage from the proximal articular surface of the tibiotarsus. No staining.
Views in usual light, in polarized light and maximim and minimum brightness of images from all the span of polarizer rotation angles. One specimen on 2 different magnifications.
Chicken from a shop, cartilage and underlying tissues from proximal articular surface of the femur. Section in the plane encompassing femur and tibiotarsus. No staining.
Chicken from a shop, cross-section of the humerus (place of beginning of a small ridge).
The specimen was stained with methylene blue and embedded into cyanoacrylate for grinding. This glue is a good embedding medium for usual microscopy, but I do not recommend it for polarized light microscopy: it is optically active and spoils the picture.
