On their website (link above), Sotheby's published a photographic portrait of three aristocratic ladies wearing tiaras, dated 1950 and entitled "Les Trois Diadèmes"/"The Three Tiaras", by French photographer Robert Doisneau. The lady in the middle wears the Courval pearl and diamond tiara, which gives us a good idea of how this tiara looks when it is worn.
But I have also been intrigued by the tiara worn by the lady on the left: I am sure I have already seen this tiara, but I do not remember where. Does anyone know which tiara it is, and who is the lady wearing it?