metallography dot com logo This is a continuation of the article by Janina Radzikowska, Senior Metallographer, The Foundary Research Institute (Instytut Odlewnictwa) Kraków, Poland . It was originally published by Buehler in Tech-Notes, Volume 2, Issue 2. It is reproduced here with the kind permission of the Editor, Mr. Vander Voort who granted it while still with Buehler.

Crossed-Polarized Light
Examination of graphite in crossed polarized light requires a very well-prepared specimen; otherwise, the matrix phase exhibits a heavy scratch pattern, and the graphite growth pattern will not be visible. Minor scratches can be tolerated in routine work.
graphite nodule blue background
graphite nodule 800x
graphite nodule magenta background
graphite nodules 250x
The polarizer and analyzer filters are placed in the crossed position (i.e., 90° to each other which produces the darkest matrix appearance), and a sensitive tint plate (lambda plate) may be inserted to further enhance coloration.The lambda plate may be adjustable on some microscopes which changes the color pattern, as illustrated in Figures 9a and b. Personally, I prefer to set the background color to magenta, as in Figure 9b. Working at a very high magnification, Figure 9c, provides more structural detail than at low magnification, Figure 9d, but requires high quality, stress- free objectives. Note the classic cross pattern seen at low magnification, Figure 9d.
Flake graphite can also be studied using polarized light, such as illustrated in Figure 10. The color varies with the crystallographic orientation of the graphite, and some internal details of the flake structure are better revealed in color. flake graphite, crossed polars+s.t. plate 200x


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