This study examines windows made using the dalle de verre technique as part of a project focused on non-invasive and micro-invasive methods for assessing their state of preservation. Non-invasive techniques help compare visible signs of degradation with structural details, such as the location and depth of steel rebars, corrosion activity, and the thickness of glass elements. However, analyzing micro-samples is still necessary to assess internal damage and the compatibility between the glass and cement mortars. This article specifically looks at the microstructure and weathering of mortars and glass fragments of two dalle de verre windows: the ensemble of dalle de verre designed by Fernand Léger for the Church of Saint- Germain d’Auxerre in Courfaivre (Swiss Jura) and the large tripartite window by Alexandre Cingria, which once decorated the choir window of the Franciscan monastery in Fribourg, Switzerland. The mortars have variable characteristics, including the alkaline content of the cement, capillary porosity, and the potential chemical instability of hydration products when exposed to atmospheric carbonates and sulfates. Despite significant carbonation of the hydrated mortar phases and exposure to moisture, the steel reinforcement rebars show no signs of significant corrosion. Additionally, harmful reactions between alkalis in the cement and soda-lime glass are limited to a specific type of pigmented glass, which is particularly prone to leaching and corrosion.