Cup, possibly a saltcellar, comprising a gold-enamelled sculpture, studded with rubies and diamonds, and two pieces of agate. The figure is a double-tailed mermaid, with a natural-coloured gold torso and a greenish-blue, red and translucent green enamelled tail. She wears a headdress of enamelled feathers and her open arms hold aloft an agate vessel with a mount of fretted and enamelled leaves, adorned with rubies. She rests on a base formed by another piece of agate, also richly adorned. The cup is borne by four enamelled fish, possibly dolphins, with double tails, whiskers and fearsome-looking teeth. It has been regarded as a Florentine or possibly French work, made around 1590, or perhaps earlier, in the third quarter of the 16th century.

Undoubtedly the work of a great artist, this figure is influenced by the work of Cellini, although it was probably made by a French goldsmith at the time of Charles IX (1550-1574). It is related to drawings by Androuet du Cerceau, Etienne Delaune and Rosso, artists of the so-called "Fontainebleau School". Jewel-encrusted figures can be seen in the altarpiece of Christ and the Samaritan Woman at the Vienna Kunsthistorisches Museum, Kunstkammer, 1542.

The mermaid’s body is decorated with numerous overlays on the arms, breast, neck and waist, interlaced with beads, scrolled designs, and mounts containing rubies and two diamonds, all that remains of the original five: on her breast, a flat-backed pear-shaped diamond, and at the waist a lozenge-cut diamond.

According to the 1746 inventory, this piece once boasted 184 precious stones: 179 rubies and five diamonds. Today, it still has 177 rubies and two diamonds. The dolphin that once fitted between the mermaid’s legs is also missing. In 1746, the head and tail were described as being of a pearly colour. The state of the work in the 19th century can be seen through the photography of Juan Laurent Minier, "Salière onys oriental, montée sur une sirène d’or, montures d’or émaillè et pierreries. XVIe siècle, règne de François 1er", circa 1879, Museo del Prado, HF0835/21.