This is a slide I am including because it is unusual, not for the amazing images of the diatoms in contains. As far as I can tell it has three diatoms. Normally these pyritized diatoms are shown on an opaque background, so this way of shows them in a different way.
Labelled as diatoms coated with Iron Pyrites, from London Clay. Big crack across the coverslip. No makers name but I am fairly sure based on the style that this was made by Laurence Hardman. The name tag is J. Lizars. This is not the slide maker, but the slide seller.
Olympus BHB microscope using 450nm LED light. As well as the large field of view image with a 4x Nikon Plan Apo NA 0.2 objective (see the crack running vertically in that image), I did a close up of the one next to the crack with a 20x Nikon Plan Apo NA 0.65 objective. Olympus Aplanat Achromat condenser, brightfield lighting. Monochrome converted Nikon d850 camera. 2.5x Nikon CF PL photoeyepiece. Single image. Doesn’t show a lot as presumably the iron pyrites is very opaque, but you can see some diatom structure in there.
In addition to the image using 450nm I also tried one with 850nm light (I read somewhere that iron pyrites is a bit more transparent in the infrared, so thought it was worth a try). Not really a huge improvement but the image was a little lower contrast and some of the structure was more visible. However this could have been at least partially due to where on the diatom I focused for the two images. Interestingly, there was virtually no focus shift between 450nm and 850nm with the 40x Leitz Plan Apo. Apochromatic indeed (well done Leitz).