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The Michel-Lévy Interference Color Chart – Microscopy’s Magical Color
Key
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John Gustav Delly, Scientific Advisor, Hooke College of Applied Sciences, Westmont, IL |
Editor's Note:
The figures in this article are included to support the text and are intended
for online viewing only. We make no claims to the accuracy of the colors
or readability of the charts online or if printed due to the wide variety
of monitors and printers available for use today. Print versions of the
Michel-Lévy charts are available as referenced in this article
as well as from several microscope manufactures and their representatives.
The Michel-Lévy Interference
Color Chart has been in continuous use by analytical microscopists for
115 years. Why such endurance? Because this chart, also known as the
Michel-Lévy Table of Birefringence, is just as useful today as it was
over a century ago in unlocking the many mysteries of microscopic particle
analysis and identification. This extraordinarily valuable aid to the
polarized-light microscopist graphically relates the thickness, retardation
(optical path difference), and birefringence (numerical difference between
the principal refractive indices) for particular views of transparent,
colorless or colored substances. These characteristics allow unknown
materials to be identified; additionally, they provide important optical
information about those materials whose identity is known.
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figure 1
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The Michel-Lévy Interference
Color Chart was first introduced to the world in a book published in Paris
in 1888 (1). This book (Figure 1) was called Les Minéraux
des Roches, and was devoted to the subject of rock-forming
minerals. In Part I, A. Michel-Lévy described the methods used by mineralogists
and chemists in the microscopical study of minerals, and, in Part 2, Michel-Lévy,
together with Alf. Lacroix, tabulated the physical and optical properties
of the rock-forming minerals. Michel-Lévy acknowledges the work of previous
investigators, including his friend and mentor (“mon maître et ami”) F.A.
Fouqué, with whom he had collaborated in the production of the two-volume,
Minéralogie Micrographique; Roches éruptives
Françaises (1879), with its beautiful atlas of 55 chromo-lithographed
plates; Des Cloizeaux, Manuel de Mineralogie (1862);
Mallard, Traité de Cristallographie (1884); DeLapparent,
Cours de Minéralogie (1884); and even Rosenbusch,
whose second edition of Mikroskopische Physiographie had
come out in 1885; Klement and Renard’s Reactions Microchimiques
(1886) and their predecessors are acknowledged for their microchemical
contributions. But now, in this 1888 book, we see in color, for the first
time, Michel-Lévy’s “Tableau Des Biréfringences” (Figure 2). The
chart is a large (about 24" X 18") chromo-lithograph based on
a water-color original; it folds in half, bottom-to-top, and then folds
four times, accordion-like, and is tipped in at the back of the book.
It is rare to find these charts that are not in need of some repair, as
the paper quality was not good, and they cannot now take repeated folding
and unfolding. We will come back to this chart’s history, and to the
others which followed it, presently.
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