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The Dispersion Staining Technique and Its Application to Measuring Refractive Indices of Non-opaque Materials, with Emphasis on Asbestos Analysis


2022, Volume 69:2, pp. 51-69


Shu-Chun Su, Ph.D.

Refractive index (RI) is the most important optical property of non-opaque materials. It is the leading diagnostic optical property of non-opaque materials, especially asbestos minerals. Dispersion staining (DS) has been proven to be the most effective technique with desirable accuracy for the measurement of asbestos minerals’ RI using the immersion method by polarized light microscopy (PLM). This paper presents a practical procedure for this measurement. To facilitate the analysis, two comprehensive suites of pre-calculated look-up tables for the conversion of the observed matching wavelength to RI were constructed for the two major types of RI liquids: Cargille Laboratories (Cargille) and Delaware Research Institute of Microscopy and Material Characterization LLC (DRIMMC), respectively, covering the range of RI liquids suitable for analyzing the six regulated asbestos minerals. RI liquid calibration in the absence of an Abbe refractometer is discussed. An alternative solution using Cargille optical glass standards is proposed, and two comprehensive suites of pre-calculated look-up tables for both Cargille and DRIMMC liquids are included, covering the range of RI liquids routinely used in the analysis of the six regulated asbestos minerals.

Download/view conversion tables (PDF):
Cargille Asbestos RI Measurement
DRIMMC Asbestos RI Measurement
Cargille RI Liquid Calibration
DRIMMC RI Liquid Calibration

CORRECTIONS: On page 59 of the published article, the Figure 7 illustration is an error and does not depict the “light path of the phase contrast microscope,” as stated in the caption. It is the light path of a darkfield microscope.

On page 63 of the published article, the temperature ranges are incorrect for Table 5. λm and t to RI Conversion for Chrysotile in Cargille 1.550 (E). The correct temperature ranges are 17° to 29° C.
Download/view the PDF of the corrected Table 5

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