Rose diamond and cobalt glass ‘bague au firmament’ or ‘ring of heavens’ portraying stars in the night’s sky. c.1780.
Beautiful,octagonal bezel with a central domed rose diamond surrounded by tiny rose diamond ‘stars’ and a border of diamonds.
High carat gold replacement shank.
1inch by 3/4 inch. Size 8. 
Such large scale rings became fashionable in France from around 1785 when  a coloured (usually blue) paste ground was studded with stones, scattered like stars in the nights sky. In 1778, the long awaited news of the pregnancy of French queen Marie Antoinette popularised these styles and the birth of her first son in 1781 by 'bagues a l'enfantement' the same style  ring but with a single central stone.