The principle of the method specified is reducing the iron in the extract solution, complexing, extracting the complex into chloroform and measurement of the optical density of the resulting colour complex by means of a molecular absorption spectrometer at 533 nm or evaporating with hydrofluoric and perchloric acids, dissolving of the residue in hydrochloric acid, measuring the absorption using a flame atomic absorption spectrometer at 248,3 nm. Measures the concentration of iron, expressed as its oxide Fe₂O₃. Applies to the analysis of extract solutions obtained from any kind of glass or glassware.