Direct solid quantitative analysis of glass by radio frequency (rf) glow discharge-optical emission spectrometry (GD-OES) by using special silicate glasses of very different composition (e.g., the SiO(2) content varied from 10 to 70%, the CaO content from 0 to 25%, the Na(2)O content from 0 to 15%, the K(2)O content from 0 to 19%, etc.) for calibration is investigated in detail. The effect of sample thickness is studied by using calibration standards and samples of different thickness than that considered as "standard" in our experiments (3 mm). Considering the variable concentrations of easily ionized elements present in the different glass specimens, measurements of the Mg(II) 280.27-nm/Mg(I) 285.21-nm line intensity ratio for the calibration standards and samples containing magnesium were carried out to check the plasma robustness. Results showed that this indicator value remained virtually constant for all the glasses assayed. The proposed quantification scheme is based on the "constant emission yield" concept in which the measured analytical signals were corrected for thickness differences relative to the 3-mm "standard thickness". In addition, better fittings to linear plots were obtained when using discharge Ar emissions as the reference signal. Results for the simultaneous determination of the glass major components (SiO(2), Na(2)O, CaO, MgO, Al(2)O(3), and K(2)O) by rf-GD-OES in two samples of different thickness (3 and 1.1 mm) showed good agreement with the expected results.