A strew slide of diatoms from pond water (including Amphipleura pellucida). Mounted in Dirax, and prepared by Brian Darnton. More in Dirax in a minute. Olympus BHB microscope using 450nm LED light. As well as the arrangement I imaged an Amphipleura pellucida using a 63x Leitz Pl Apo 1.4 objective, oil immersion. Olympus Aplanat Achromat condenser, oil immersion, oblique lighting. 2.5x Nikon CF PL photoeyepiece. Monochrome converted Nikon d850 camera. Single unstacked image. Striae spacing measured at 256nm (39.1 per 10µm).
Amphipleura pellucida (Kützing) Kützing 1844. Published in: Kützing, F.T. (1844). Die Kieselschaligen Bacillarien oder Diatomeen. pp. [i-vii], [1]-152, pls 1-30. Nordhausen: zu finden bei W. Köhne. Page 103, Plate 3 Figure 52, Plate 30 Figure 84.
So, Dirax. Before this one, I had heard of Darax, but Dirax was a new one on me. It’s quite a high refractive index mountant, but has yellowed. It is mentioned in the article “A history of Northern Biological Supplies (NBS)” by J. Eric Marson, and downloadable from the Quekett Microscopical Club site here. It is a high refractive index mountant (as expected) and was introduced for use with ‘larger specimens’. It is also mentioned in “OBSERVATIONS Some works by Douglas Turnbull Richardson” (see here) where it is described as “Stryax (storax) resin 55 : Chloroform 45 (by weight)”, and “Dirax Diatom Mount Gum Styrax (Storax) is a naturally occurring fragrant gum resin from the Styrax officinalis bush and it is used in medicine, perfumery and incense. It is recommended for use as a diatom mountant as far back as 1891 (The Microscope and its Revelations, Carpenter and Dallinger 7th. edition pp 444, 445). It’s disadvantage is its very dark colour.”. Dirax does not seem to have been widely adopted, as this is the first (and only) one I have seen so far.