An arrangement of Coscinodiscus asteromphalus. Prepared by Watson and Sons Ltd. Mounted in Cassia Oil (more on that in a minute). Olympus BHB microscope. Canon EOS 5DSR camera using white LED light and auto whitebalance. 10x Nikon Plan Apo NA 0.45 objective. Olympus Aplanat Achromat condenser, brightfield lighting. 2.5x Nikon CF PL photoeyepiece. Single image (not stacked). I do not have a remote release for the Canon camera and I got too much movement between images for stacking to work successfully, hence a single image. Imaged in white light and left as a colour photo given the orange hue from the Cassia Oil.
Why Cassia Oil as a mountant for diatoms? It’s refractive index is approximately 1.60, which is nice and high compared with diatom frustules (about 1.43) giving lovely contrast. Not widely used as far as I can tell, but was used occasionally.