The finishing of the main rooms on the second floor of the Cameron Cold Bath was given special importance: the interiors of the Agate Rooms are decorated with marble, paintings, gilded bronze, parquet flooring, and colored Ural and Altai jasper, which Russian craftsmen of the 18th century worked with exceptional skill.

The deposits of hard colored stones were discovered in the Urals as early as the 16th century, but at that time the methods of processing them were not yet known. Emperor Peter I showed great interest in the use of "colored stones" in the decoration of palace interiors, laying the foundation for the development of lapidary art in Russia. By his decree, in 1725, the first faceting factory in Russia was opened in the suburb of St. Petersburg — Peterhof — where products made of colored stones began to be manufactured and craftsmen were trained in the art of stone cutting. By the mid-18th century, an interest in mineralogy had spread among the Russian aristocracy. In 1765, by order of Empress Catherine II, an expedition led by Dannenberg was sent to the Urals, which discovered new deposits of jasper, agates, carnelian, and other minerals. By the early 1780s, Russian faceting factories had developed technology for producing items from hard gemstones, and the long-held dream of decorating palace halls with natural colored stone became achievable.

Cameron built the Cold Bath in 1780–1781 and began the finishing work in 1782. In the spring of 1783, he received an order from Catherine II to change the design of the decoration of two cabinets on the second floor of the Cold Bath and prepare a project for their jasper decoration. According to the new project, the walls of the cabinets were cut down by nine centimeters and covered with limestone slabs faced with jasper using the technique of "Russian mosaic." The final work — grinding and polishing the colored stone, intended to reveal the brightness of the colors and richness of the tones — presented particular difficulty. The polishers had to bring about two hundred square meters of walls, casings, and cornices to a glassy shine. This work was done manually by Russian craftsmen. Since the widely used Urazov jasper in the decoration was called "meat agate," the name "Agate Rooms" eventually became established for the entire pavilion, although the lower floor continued to be called the Cold Bath. During the Great Patriotic War and occupation, the artificial marble and jasper facing on the walls and door panels of the Agate Rooms were severely damaged. A significant part of the gilded bronze ornaments decorating the walls and doors of all rooms, some bronze branch-lamps, and bronze medallions from the pedestals in the Large Hall, as well as bronze Rashetov bas-reliefs from the walls of the Jasper Cabinet, were lost. Many marble sculptures and six jasper vases disappeared without a trace. However, despite the great losses, the decoration of the Agate Rooms has largely been preserved since the 18th century and is an example of a unique artistic tradition without analogues in the history of world art.

Restoration work in the Agate Rooms was completed in September 2013.

Sources:

https://www.tzar.ru/objects/ekaterininskypark/cameron/agathrooms

https://ru.wikipedia.org/wiki/Cold_Bath_with_Agate_Rooms