Left: microscopic image of the crystals without polarized light (dark field)
Right: microscopic image of the crystals with polarized light
The pictures above are produced when I sandwich the crystals between the glass slide and the cover. However, Microscopy UK shared that their slides were prepared by melting the crystals (sandwiched between the slide and cover) using an alcohol lamp. I wasn't confident in using the lamp, so I used the hot plate instead. When the crystals melt, the slides are removed from the hot plate and it will quickly re-crystalize into a thin film. Interestingly, the images from the slides I've prepared are very different from those in their website, likely because of the environmental factors influencing the formation of the crystals as they cool.
Left to right: salicylic acid, tartaric acid, sorbic acid
These are how the thin crystal layers look under a polarized light microscope. Aren't they pretty?