One of the prettiest tiaras, that we know, is the diamond and aquamarine diadem in kokoshnik design from the Swedish royal family.
I found a match in the design sketches of the workshop Friedrich Kreuter & Co Hanau, Archive, made by their Designer Wilhelm Homburg on 8./9. May 1908.
He designed 5 sketches for a first view to set five (smaller) oval Aquamarines in a tiara with a fine diamond trelliswork.
The Aquamarine Kokoshnik was later made with 5 larger oval facetted Aquamarine and a smaller but higher trellis ornament between, as in the first sketch, for the Crown Princess Margareta of Sweden, Princess of Connaught.
It’s known Crown Princess Margareta Margaret Victoria Charlotte Augusta Norah; 15 January 1882 – 1 May 1920) was Crown Princess of Sweden as the first wife of the future King Gustaf VI Adolf. She was the elder daughter of Prince Arthur, Duke of Connaught, third son of Queen Victoria of the United Kingdom, and his wife Princess Louise Margaret of Prussia. Known in Sweden as Margareta