Cameron paid particular attention to the state rooms on the upper floor of the Cold Bath: the interiors of the Agate Rooms are decorated with marble, painting, patterned parquets, coloured Urals and Altai jasper that eighteenth-century Russian craftsmen worked with exceptional mastery.

Deposits of hard semiprecious minerals were discovered in the Urals as early as the sixteenth century. Peter the Great displayed a great interest in the use of such “coloured stones” to finish palace interiors and laid the foundation for a stone-cutting industry in Russia. On his orders the first lapidary works in Russia was opened at Peterhof, a suburb of St Petersburg, in 1725 and began to produce articles from attractive minerals and to train craftsmen in the art of stone-cutting.

In the middle of the eighteenth century an interest in mineralogy became common among the Russian aristocracy. In 1765, on the orders of Catherine II, an expedition led by Yakov Dannenberg was dispatched to the Urals, where it discovered new deposits of jasper, agate, cornelian and other minerals. By the early 1780s Russian lapidary works had developed the technology to make articles from hard semiprecious stone and the long-cherished dream of decorating palace halls with natural coloured stone became a real possibility.

In the spring of 1783 Catherine II instructed Cameron to prepare a plan for the decoration of the upper floor using jasper. The architect obeyed the Empress’s wishes and prepared designs for two jasper cabinets. In accordance with this project twelve centimetres of masonry was knocked off the walls of these small rooms; they were then covered with limestone slabs and faced with jasper using the “Russian mosaic” technique. The main difficulty was the finishing work – grinding and polishing the coloured stone in a way that would bring out its bright colours and rich tones. The polishers had to give a mirror-like sheen to around two hundred square metres of walls, architraves and cornices. Russian craftsmen carried out this work by hand.

The walls of two rooms on the upper floor were lined with sheets of dark red Urazovo jasper with quartzite inclusions that was called “meat agate” in the eighteenth century. That was why the interiors that Cameron created became known as the Agate Rooms.

During the Second World War and the Nazi occupation the artificial marble and jasper facing on the walls and doors of the Agate Rooms suffered badly. A considerable portion of the bronze ornaments adorning the walls in all the rooms was destroyed; many marble sculptures disappeared without trace, as did six jasper vases, nine bronze basreliefs from the walls of the Agate Cabinet and bronze medallions from the bases of torchères in the Large Hall. Yet, despite the major losses, the eighteenth-century décor of the Agate Rooms has in the main survived and is an embodiment of a unique tradition unparalleled in the history of world art.

The Agate Rooms were restored in 2010–2013 with donations from Russian Railways and TransSoyuz Charitable Foundation.