The weathering of glass exposed to an urban atmosphere was studied through an in-field experiment using two low durability alkali rich glasses. The glasses were exposed according to two modes: sheltered or unsheltered from direct rain, and during two exposure periods: from November 1997 (over one year) and from May 1998 (over three months). Infrared spectroscopy, analytical scanning electron microscopy, electron probe microanalysis and secondary ion mass spectrometry allowed the authors to characterise the formation of a leached hydrated layer in the surface of the samples. This layer developed whatever the season and exposure mode. This underlines the role played by all water suppliers: rain, but also humidity. The action of the latter is not negligible. The weathering is more pronounced in winter when rain and humidity are high.
