Potash-lime-silica glasses typically used in medieval stained glass north of Alps show a low chemical durability due to the low silica content and the high amount of potassium, sodium and other network modifier ions such as Ca or Mg. This glass is sensitive to acidic conditions typical of polluted environments; it is therefore easily damaged due to the ion exchange process which leads to the formation of a superficial layer with chemical and physical characteristics different from those of the bulk glass. The effect is a hazy appearance, flaking phenomena and the formation of corrosion products. The studies of the mechanisms leading to those effects, particularly dangerous for cultural heritage glass objects, are important to introduce procedures to slow down these reactions and to develop protective methods. Different techniques were applied such as IRRAS to monitor the changes in composition after leaching and weathering and ToF-SIMS to determine the ion migration due to the exchange processes. The resistance of those glasses to acidic solutions was tested and SO2 mixed with different amount of RH were used. The results showed a strong dependence on the glass composition, time, pH, and type of acid used. The applicability and the efficacy of a protective sol-gel silica coating were tested. It consists of an inorganic and transparent layer (300 nm) applied without any heating treatments. It was proved that it enhances the resistance of the glass avoiding cracking and minimizing the formation of weathering products.