The principle of the method specified is spraying the extract solution into the flame of the burner of an emission or absorption spectrometer, if necessary with the addition of a spectrochemical buffer solution, or into the flame of a filter flame spectrometer without this addition. For FES and FAAS, the lines at 589,0 nm and 766,5 nm, respectively, are used and compared with the measurements of reference solutions, for a flame filter spectrometer, the specific filters are used. Measures the concentrations of sodium and potassium, expressed as their oxides Na₂O and K₂O. Applies to the analysis of extract solutions obtained from any kind of glass or glassware.