Successful operation of conventional as well as advanced coal combustion systems depends on controlling and minimizing the development of ash fouling and stagging, i.e., fireside deposits. The development of these deposits depends not only on combustion design and operating conditions, but also on the composition and quantity of the inorganic species in the coal. Coals contain several minerals, and low-rank coals contain organically associated cations that vary in their association, size, and position relative to one another and in their composition. In the course of combustion, the major inorganic constituents directly affect chemical and physical transformations, such that inorganic species are initially partitioned into gaseous, liquid, and solid intermediates. this report discusses the design and construction of an infrared emission sampling probe for ash deposits, and discusses the correlations of ash build-up with the emission spectra.