A strew slide of Amphipleura pellucida (and a few other species) mounted in Realgar (Arsenic sulphide). Dated 1/1/[19]03. Prepared by William Gatrell, however the date puts this as just after his death in 1902 (more on him, his life and work, here). Olympus BHB microscope using white and 450nm filtered LED light. Canon EOS 5 DSR camera. White light images whitebalanced in Darktable. 450nm light image processed in Photoshop (desaturate, sharpen denoise etc). Wider strew imaged with a 20x Nikon Plan Apo NA 0.65 objective, and brightfield lighting. Higher magnification images with a 63x Leitz Pl Apo NA 1.40 oil immersion objective, oblique lighting (orientated parallel to the long axis of the diatom to emphasize the striae). White light and 450nm light. Olympus Aplanat Achromat condenser, oil immersion for the 63x objective. 2.5x Nikon CF PL photoeyepiece. Single images (no stacking).
I like Realgar slides (and have published an article on them in the Quekett Journal). They are high contrast due to the high refractive index of the mountant, as can be seen with the 20x image above. However they do have one major issue – the yellow colour makes using shorter wavelengths of light ‘a challenge’, so maximum resolution cannot always be realized compared with some mountants. For example with this slide and the 63x objective, the white light image had an exposure time of 1/640s while the 450nm light exposure time was 1/2s. These slides can also suffer from degradation of the Realgar. There are some issues with this one, but the majority of it is still good.