Following the rigorous and meticulous removal of the stained-glass windows, the restoration chain continues in the Vitrail France workshop in the Sarthe region. Stained-glass glaziers specialising in pathology take charge of restoring the glass: "here the panels are considered as patients who are ill and in need of treatment". First they are covered with compresses moistened with water and sodium thiosulfate, then cleaned locally with a cotton swab on a baton. The cotton is moistened with a precise mixture of demineralised water, acetone and ethanol. Each time the swab is applied, the cotton is blackened with the grime of the years. With the patience of a saint, the stained-glass glaziers apply and re-apply spotless swabs of cotton until they remain white, a sign that the cleaning is complete.
Next comes the intervention of the surgeons, who operate on fractures and establish grafts. By soldering with copper and tin or by applying silicone, no efforts are spared to repair and consolidate the glass, the goal being for the interventions to be reversible and invisible. In the extremely rare case of a missing part, grafts are made. The new glass is crafted to correspond to the missing shape. It is then tinted, the glass being covered with pigment mixed with water and fired at very high temperatures. Yellow is thus obtained from silver salts fired at 660°, blue from enamel fired at 580° and black is obtained from grisaille fired at 580°. Pieces with several colours are fired several times. Mastered to perfection by the painter-glaziers, this know-how is situated at the frontier between art and physics-chemistry.
Cleaned, repaired, then assembled with pieces of lead, all the stained-glass windows leave this hospital-workshop stronger and more beautiful, ready to resume their place in the windows and illuminate and magnify the interior of the Chapelle Royale.