The Microscope - Volume 57, Fourth Quarter 2009

IN THIS ISSUE:

On the cover: Examples of natural snow crystals exhibiting triangular morphologies. The equivalent diameters range from 1 to 3 mm. The lower right example shows a crystal with an initial truncated triangular morphology (outlined by the central surface markings) that subsequently grew plate-like branches. See “Aerodynamic Stability and the Growth of Triangular Snow Crystals” by K.G. Libbrecht and H.M. Arnold.

Editorial: PLM and Dispersion Staining Through the Years

Gary J. Laughlin
The Microscope. 57 (4), p ii
Excerpt: Because The Microscope has published so many papers on the topic of dispersion staining, and the McCrone Research Institute in Chicago teaches the subject in nearly all of its PLM courses, I am often asked if Dr. McCrone invented the technique. Of course he didn’t, but he did help coin the term and discover the most practical analytical use for it. And through McRI he trained the greatest number of practitioners of PLM and DS for the purpose of identifying asbestos. Full article (PDF)

Dispersion Staining Using a 1.2-1.3 NA Cardioid Darkfield Condenser

Theodore M. Clarke
The Microscope. 57 (4), pp 147-153
Abstract: A 2007 Inter/Micro presentation and subsequent article in The Microscope demonstrated that the LOMO darkfield cardioid condenser provides good darkfield when used with the 60× 1.00 NA LOMO apochromatic objective, with the punctae of diatom Frustulia rhomboides resolved. A presentation at Inter/Micro 2009 demonstrated dispersion staining with the same combination of condenser and objective, which is the subject of this article. Comparable imaging was obtained with the 90× 1.25 NA LOMO achromatic objective when the funnel insert (NA-reducing cone) for this objective, included with the condenser, had the end bore diameter increased by 20%. Uniform darkfield required more precise centering of the reduced diameter at the end of the funnel insert. This precise centering was obtained with a homemade insert that has a closer fit to the guiding surfaces in the bore of the 90X objective. Full article (PDF)

Dispersion Staining and Nelson Dodge

Anthony A. Havics
The Microscope. 57 (4), pp 155-156
Excerpt: The concept of dispersion staining began with Christiansen in November, 1884, consisting of experiments with white powder refractive index determination by the liquid immersion method. In 1885, Lord Rayleigh remarked on this as the “Christiansen effect” in a paper published in Philosophical Magazine. It was later recognized by Winchell in two papers in the American Mineralogist (1929 and 1947) that dispersion of refractive indices and the ratio of birefringence-dispersion were diagnostic. In 1942, Wardlow recognized that coloration from dispersion could be used for identification of quartz in samples to be analyzed for silica dust content. It was immediately after Crossman’s initial papers on dispersion staining in 1948 that the Nelson Dodge article appeared followed by Emmons in the same issue. Full article (PDF)

Aerodynamic Stability and the Growth of Triangular Snow Crystals

K.G. Libbrecht and H.M. Arnold
The Microscope. 57 (4), pp 157-163
Abstract: We describe laboratory-grown snow crystals that exhibit a triangular, plate-like morphology, and we show that the occurrence of these crystals is much more frequent than one would expect from random growth perturbations of the more-typical hexagonal forms. We then describe an aerodynamic model that explains the formation of these crystals. A single growth perturbation on one facet of a hexagonal plate leads to air flow around the crystal that promotes the growth of alternating facets. Aerodynamic effects thus produce a weak growth instability that can cause hexagonal plates to develop into triangular plates. This mechanism solves a very old puzzle, as observers have been documenting the unexplained appearance of triangular snow crystals in nature for nearly two centuries. Full article (PDF)

Forensic Applications of the Transmission Electron Microscope

Whitney B. Hill
The Microscope. 57 (4), pp 165-170
Abstract: Transmission electron microscopy (TEM) is rarely used as an analytical tool in forensic science, and consequently there is no standard method on how to conduct trace evidence analysis using TEM. This article will introduce a newly developed method specifically for forensic trace evidence analysis done by TEM. This article will also explain the ongoing development of a TEM database containing known particles of various types. The purpose of the particle database is to be used as a reference for particle identification when conducting forensic trace evidence analyses via TEM. Full article (PDF)

Book Review: More Theory Than Meets the Eye

Light and Video Microscopy (Academic Press), by Randy Wayne
Review by Christopher S. Palenik
The Microscope. 57 (4), p 171
Excerpt: I showed this book to several microscopists and a class of students studying pigment microscopy and asked them what they would expect to see on its pages based on the appealing title and cover image. The responses were universal and included: “a book with lots of pictures” and “a book about digital and video imaging.” The cover, which hints at an atlas of color images and a primer on digital imaging techniques, actually yields to a survey of image formation and light microscopy theory. The digital and video imaging section is limited to Chapter 13, and there are only two color plates in the entire book. Full article (PDF)

The Microscope Past: 35 Years Ago — Recent Applications of High Voltage Electron Microscopy in Various Branches of Science

C.J. Humphreys
The Microscope. 57 (4), pp 179-185. Originally published in The Microscope, Vol. 22 (2), 1974.
Abstract: This review paper outlines some of the advantages of the high voltage electron microscope over conventional 100 kV microscopes and briefly describes some recent applications in various branches of science. In particular, penetration, resolution and radiation damage are considered, and some recent applications to biology metallurgy, mineralogy and solid state physics are discussed. Full article (PDF)