•Reflectance spectra of synthetic glasses of basic igneous compositions are measured.•Optical constants are retrieved by Hapke modeling from the measured spectra.•Particle sizes are estimated using the optical constants to fit measured spectra. Silicate glasses with igneous compositions can be an important constituent of planetary surface material via effusive volcanism or impact cratering processes. Different planetary surfaces are mapped with hyper-spectrometers in the VNIR, and in this spectral range crystal field absorptions are useful in discriminating iron bearing silicate components. For these reasons studying glassy materials, and their optical constants, is an important effort to better document and understand spectral features of Solar System silicate crusts where glasses are present, but may be difficult to map. In our work we present a set of four different synthetic glasses, produced under terrestrial conditions, with variable composition and in particular an increasing amount of iron. The VNIR spectra show, for all the compositions, two absorptions are present near 1.1 and 1.9μm but reflectance, slope and absorption shape varies with composition. We measured the reflectance of different particle sizes of the samples and used radiative transfer models to estimate the optical constants as a function of wavelength. We used the retrieved optical constants to estimate the particle size from the measured reflectances and the results fall within the known sieve range. We qualitatively discuss the effect of the shape and distribution of particles on the application of the model.