Some agate jewelry made between 1842 and 1883 bears the diamond-shaped British Registry mark, however, as the makers rarely signed their work, little is known about the makers. A study of catalogs listing the international exhibitors attending The International Exhibition of 1851, in addition to a study of individual pieces in 1862 and 1867, it was discovered that the most important makers were ‘Muirhead’ of Glasgow, ‘G.& M. Chrichton’, ‘McKay and Cunningham’, ‘Marshall and Sons’ and ‘Meyer and Mortimer’ of Edinburgh. From Aberdeen were ‘Jamieson’ and ‘M. Rettie and Sons’ from Birmingham were ‘Bradford’ and ‘Unite’ and ‘Ellis and Sons’ of Exeter, only half of which consistently signed their jewelry.
One of the earliest designs is the faceted agate cylinder bracelet, known as a ‘barrel’ bracelet from the 1840′s mounted in gold or silver caps at both ends. Some pebble jewelry is slate-backed, openly mounted on a slate, held together with tiny silver or gold claw-prongs.
Engraving usually incorporated floral, foliate and geometric designs and it is not unusual to see different patterns on different links of a bracelet. Elaborate was substituted by plain setting in the last two decades of the 19th century, as had been illustrated by ‘Rettie’ and ‘Jamieson’ in the mid 19th century, and the outer silver frame extended to a bezel or inner frames separating the stones.
Artificially stained agate was used in cameo carving and gem engraving in Italy from the 1860′s. Staining was done by placing the stone in a sugar solution, which absorbed and fired to burn the sugar, staining the layers of agate black or dark brown. Metallic salts were used to impart artificially the colors of carnelian and chrysoprase. The white, non-porous part of the stone was then carved against the dark background.
Naturally composed of parallel layers in varying shades of black, brown and white, banded agate was artificially colored by steeping it in honey and sulfuric acid. It is then heated to release carbon and the absorbent part assumes a black color.