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The Microscope - Volume 70, Third Quarter 2023


On the cover:
Photomicrographs of a glass standard in Cargille High Dispersion refractive index liquid showing the relationship between the matching wavelengths and central stop dispersion staining colors and corresponding Becke lines. See The Unification of Becke Line and Dispersion Staining Techniques for the Determination of Refractive Index of Non-Opaque Materials, page 99. (Courtesy of Mickey E. Gunter).

Editorial | Another Leeuwenhoek Comes to Light

Dean Golemis
The Microscope 70:3, p. ii, 2023

Excerpt: Antony van Leeuwenhoek’s handmade microscopes — those simple, single-lens instruments small enough to rest in the palm of your hand — continue to intrigue and fetch large sums at auction. The Dutch microbiologist is known to have left 247 microscopes when he died in 1723. And now, one more has surfaced.

The Unification of Becke Line and Dispersion Staining Techniques for the Determination of Refractive Index of Non-Opaque Materials

Shu-Chun Su, Ph.D.
The Microscope 70:3, pp. 99 – 112, 2023

Abstract: Becke line and dispersion staining are the two major techniques for measuring the refractive index of non-opaque materials by the immersion method via polarized light microscopy. The immersion method has wide applications in many scientific disciplines that require the refractive index measurement of natural or man-made materials, such as geology, material science, biology, pharmaceutical science, forensic science, etc., and especially in the environmental science to identify asbestos minerals in building and construction materials as well as in their natural occurrences. Based on the two techniques’ inherent relationship, this paper presents a unified quantification diagram applicable to both Becke line and dispersion staining techniques for the measurement of the refractive index of non-opaque materials. Issues relevant to the application of Becke line and dispersion staining techniques are discussed in detail. Also presented is a suite of tables, charts, and illustrations to facilitate the refractive index measurement of asbestos minerals.

What We See Part 3: Interface Between Particles and Mounting Media in a Fixed Mount

Russ Crutcher and Heidie Crutcher
The Microscope 70:3, pp. 113 – 126, 2023

Abstract: The image of a particle is always affected by the properties of the medium in which they are mounted. This is the case for a particle in air or any other mounting medium. It is the image of the particle that is seen, and if the mounting medium is changed, then the particle image is altered. A (colorless) particle in a fixed mount is visible as a result of the size, shape, and differences between the refractive index of the particle and the refractive index of the mounting medium. The properties of the mounting medium become the reference by which the properties of the particle are measured. If the particle is already fixed in an adhesive layer, as is the case with a sticky-tape lift, then knowing and matching the refractive index of the adhesive may be a consideration to minimize artifacts that may be introduced by the adhesive. A collection of loose individual particles may be prepared in a permanent mounting medium selected for the properties of the medium itself, e.g. dispersion staining, wherein the medium may be selected to match the refractive index of a particle of interest at some wavelength. Or, it may be selected to have a significantly different refractive index to optimize morphological features, as might be the case with pollen identification. For electrically conductive particles, the refractive index is equal to the square root of the product of the dielectric constant times the magnetic permeability. The imaginary part of this calculation is the part of interest, because it is the difference in the imaginary refractive index that creates a visible effect. The selection of the mounting medium is part of the analysis, and it controls or limits the interfacial optical properties that can be seen.

Critical Focus | Aliens of the Botanical World

Brian J. Ford
The Microscope 70:3, pp. 127 – 138, 2023

Excerpt: Orchids have long been important to microscopists. The cell nucleus was first identified in orchids, and some species are so minute they require a microscope to be clearly observed.

We were hiking up the tallest mountain in Borneo when I saw it. Nestling on a rain-wet branch was the tiny but unmistakable flower of the Pinhead Orchid, Podochilus tenuis. The local botanists knew it well; it had been studied since its discovery in 1833 and measured some 2 mm (8/100 in.) across — the smallest known orchid in the world. Others have since made similar claims. When Platystele jungermannioides was recently discovered in Ecuador, it was no smaller, though was immediately claimed as the record holder. Then Campylocentrum insulare was spotted in Brazil during 2015, looking like a tiny fungus and recognizable as an orchid only under the microscope. In Australia you will find _Bulbophyllum minutissimum) less than 1.5 mm (6/100 in.) — and all these diminutive flowers have petals that are only one cell thick. These are the smallest land plants anywhere on earth.

The Microscope Past: 25 Years Ago | Electron Microscopy of Air-O-Cell® Air Samplers

James R. Millette and Pronda Few
The Microscope 70:3, pp. 139 – 143, 2023
Originally published in The Microscope, Volume 46, Third Quarter, pp. 155 – 159, 1998.

Abstract: Air-O-Cell® air quality particle samplers were developed primarily for the assessment of bioaerosols, mold spores and pollen. They are also used in the analysis of other types of airborne particles. As an inertial impaction collector, particles are caught in an optically clear sticky sampling medium layered on a glass coverslip. Electron microscopy was attempted on samples of indoor air particles collected with the Air-O-Cell® sampler. It was determined that scanning electron microscopy with X-ray analysis could be performed on particles including those opaque in the light microscope. Quantitative work was difficult because the sticky medium distorted under the electron beam. Particles caught in the sticky material could be extracted in alcohol and prepared for transmission electron microscopy, but no small particles (less than 1 µm) were found.

Afterimage | U.S. National Colors

Martin Dähnrich
The Microscope 70:3, p. 144, 2023

Microchemical tests for iron using Prussian Blue and thiocyanate reactions with Fe3+ cations. Selected as Most Unique Photomicrograph at the Inter/Micro 2023 Photomicrography Competition in Chicago.

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