This part of ISO 7404 specifies the methods for determining the reflectance of vitrinite of coals microscopically on the polished surfaces, immersed in oil. The methods are applicable to coals from single seams or coal blends covering the whole range of low-, medium- and high-rank coal. Vitrinite reflectance measurements can be used to characterize the components within blends. Measures can be taken to correct for the vitrinite percentage within each of the components of the blend or to determine the proportion of components in a blend, particularly when the components have dissimilar vitrinite contents. This method necessitates the identification of vitrinite by the analyst. Reflectance measurements on vitrinite obtained by interpreting the results from an automated system, are outside the scope of this part of ISO 7404.