@ the eyepoint
@ the EyePoint
The Michel-Lévy Interference Color Chart – Microscopy’s Magical Color
||John Gustav Delly, Scientific Advisor, Hooke College of Applied Sciences, Westmont, IL
MICHEL-LÉVY CHART TO USE
are included in almost all textbooks on optical crystallography, although
they are not always in color. We will consider here only the colored
ones. Besides the color charts in optical crystallography textbooks,
most manufacturers of polarized-light microscopes supply full-color Michel-Lévy
charts, including Olympus, Nikon, Zeiss, Leitz, and, formerly, Vickers.
Typically, the polarized-light microscopist has the interference color
chart framed, laminated, or otherwise mounted on a wall next to the microscope
where it can be conveniently and quickly consulted. The more one uses
the interference color chart, the more useful and familiar it becomes;
its potential application to the analysis of transparent substances is
Are there differences
between the interference color charts produced over the last 115 years?
Which is the best? Let’s conduct a more-or-less chronological survey
of Michel-Lévy interference color charts, starting with the granddaddy
of them all, the original one that appeared in 1888, which we already
introduced as Figure 2. This “Tableau des Biréfringences” has
thickness to 60 µm, and includes four-orders of interference colors.
A birefringence value of 0.040 marks the upper right corner of this chart.
Mineral names are located as close as possible at their characteristic
birefringence value. There are very subtle color differences in the first-order
gray-white area of the chart, and it is a great help to have the descriptive
name of the color. In the case of this original chart, there is a narrow
strip of all four orders of interference colors along the top of the chart,
together with the descriptive name of specific values of retardation.
Figure 5 is a close-up of the upper-left corner of this chart that
illustrates this feature. At about 24" X 18" in size, this
is one impressive piece of work, and the opportunity to view one in person
should not be missed.
click image to view large PDF version (972K)
was mentioned that the Third Edition of Rosenbusch’s famous text, Mikroskopische
Physiographie, was already published when Michel-Lévy’s book came
out in 1885, but by 1904 it had been expanded to a two volume, Fourth
Edition (16) in collaboration with E.A. Wülfing. Volume I, called the
first half, is devoted to morphology, and the principles of optical crystallography;
the second volume contains the data on specific minerals. In this edition,
Plate 3 (Tafel III), the Michel-Lévy chart in color is mounted at the
back of Volume I; Figure 6 is an illustration of this chart. In
the text (p. 283), it is referred to as “Die Michel-Lévysche Farbentafel”
(The Michel-Lévy Color Table), but the actual color chart (Figure 6)
is titled “Doppelbrechung und Jnterferenzfarbe” (Double Refraction and
Interference Color). This chart is 15" X 9¼"; the colored area
is 10" X 4". This chart indicates thickness to 50 µm; three
orders of interference colors, and just the start of the fourth order;
the vertical lines are at 50 nm apart, with every 100 nm numbered; birefringence
0.036 is at the upper-right corner; mineral names are located at their
characteristic birefringence, and the interference colors are named.
This ~100 year old color chart is perfectly usable today. It is printed
on card stock, and folds at two places to fit between Tables 2 and 4.
click image to view large PDF version (797K)