Later Contant d'Ivry worked for
Louis-Philippe, duc d'Orléans, for whom he transformed interiors of the
Palais-Royal, Paris, in 1754, designs that were widely admired and published by
Diderot and
d'Alembert in the
Encyclopédie, 1762, where
Jacques-François Blondel praised their "correct middle pathway between two excesses, that of the heavy weight of our ancients and that of frivolity". Surviving examples include the dining room of the Duchesse d'Orléans (now the Salle du Tribunal des Conflits of the
Conseil d'État), which is in a neo-classical style with pilasters, and another of her rooms (now the Salle des Finances), in which his surviving decoration of the ceiling and door panels is lighter and more reminiscent of the earlier
French Regency period. Contant d'Ivry was also responsible for the exteriors of the northern part of the east wing (now on the
Rue de Valois), the
avant corps of which, "with its giant balcony brackets and rather inventive detailing, combines Rococo-style decorative charm with a certain Classical solidity in its massing." staircase In 1763 a fire which started in the east wing in the opera house, the
Salle du Palais-Royal, destroyed not only the theatre but also the adjoining sections of the palace. While the municipality of Paris was responsible for the opera house and hired its own architect,
Pierre-Louis Moreau-Desproux, who also designed the new facades on the Rue Saint-Honoré side of the building, Louis Philippe engaged Contant d'Ivry, who designed the interiors of the reconstructed
corps de logis, the facades of the Cour d'Honneur (on the garden side), and a grand staircase, the "splendid ''escalier d'honneur'', [which] with its domed covering and dramatic curved descent, is justly famous." == Église de la Madeleine ==