- Castle of the Dukes of Brittany

Safeguarding the tufa stone was a major aspect of the restoration. The delicate Loire tufa, the outstanding feature of the 15th and 16th century buildings, is subject to "desquamation", a condition causing it to break off in flakes: more permeable than its neighbours, granite and Saint-Savinien stone, it had deteriorated more quickly.

The architect Pascal Prunet, working with the Historical Monuments laboratory, has developed some completely new methods to protect this stone, including desalination and consolidation.

Each moulded or carved decorative element was carefully treated based on a protocol developed with the laboratory. To draw out the salt, poultices were applied which absorbed the water held in the stone using a sprayed rock wool process.

The Nantes company Lefèvre has developed the patented Tollis method to treat large areas and prevent the migration of destructive salts. Once the stone has been desalinated and dried, a coat of milk of lime is applied which protects it from pollution, humidity and salt penetration. This protective skin will make the tufa more resistant.

It is the carved whiteness of the tufa façades which first strikes visitors as they enter the courtyard.

The stone highlights the majesty and elegance of a residential palace built to reflect ducal prestige. The main ducal residence (Grand Logis) is characteristic of the late 15th century Flamboyant Gothic, while the loggias of the Golden Crown Tower (Tour de la Couronne d'Or), built by Anne of Brittany, bear signs of the early Renaissance.