From Wikimedia.
Royal-magazin.de has this about the jewels shown in the portrait: "One of Oscar Massin's earliest designs was owned by none other than Ekaterina Chavchadze, Princess of Mingrelien, who was married to Prince David I. Daviany, living in Georgia until his death in 1853. She then took over the guardianship of their son and moved to St. Petersburg, where she became an important member of the Czar's court.
Oscar Massin, before opening up his own jewelry studio in 1863, worked as a designer and goldsmith for many well known jewelers in Paris, including the famous Lemonnier. Many of the noblest members of 19th century European aristocracy came to House Lemonnier for their jewelry. There was no doubt that here some of the finest items in the world could be obtained. While working for Lemonnier, Massin gained valuable experience dealing with the whims and wishes of the high and mighty of Europe. He became acquainted with the special, extraordinary desires of people such as Empress Eugenie and Queen Isabella II of Spain. One thing these aristocrats liked to do was to bring him their old family heirlooms, asking him to remodel them, modernize them, make them special and unique, to fit their personal wishes and tastes. Later, he would become known all across the world, delivering jewellery to the royal house of Romania, (1869), the British royal family, (1878), and even to the House of Orange-Nassau in Holland, (1881).
Lemonnier was also popular among the Russian aristocracy. During the time while he was still at Lemonnier, the Princess Ekaterina Chavchadze-Diadny showed up one day looking for something extra special. She found goldsmith-designer Oscar Massin; together they sat down to plan some fine new jewelry. In 1860 the Princess, Queen Regent of Mingrelia (1853-1866) ordered a tiara and a devant de corsage and Massin designed it.
Typical of the style at that time, it was very floral, combined with fringes. Usually the customer chose which flowers would best express her particular personality. Together they would try to tell her story using the symbolism of flowers. The use of oat sheaves in the design was a bit unusual for this time. The high point for them had been in the early 19th century; they were no longer current. It is very likely that the Princess already possessed these diamond ears of wheat and made a special request to Oscar Massin to incorporate them into his design.
The portrait shows the Duchess wearing this piece, combined with a fringe collier. The way the colllier subtly repeats Oscar Massin's oat-fringe design is beautifully effective. The large diadem and devant corsage, (18.5 cm), are mounted only with diamonds, in gold and silver. Elegant and delicate, the naturalistic panicle oats, are free to move on links as fringes and the three 'wild roses' are removable to be worn as brooches, or hairpins if desired.
Princess Catherine 'Ekaterina' (Yekaterina) was present at the coronation of Alexander II in 1856; her sister was the wife of Griboyedow, the poet and ambassador. Later she lived in St. Petersburg where she was a lady-in-waiting. Finally, she lived in Paris, but died in Martvili.