Finally I've found the information about the ruby parure. Vincent Meylan in his book 'Queen's Jewels' has this to say on page 92:
'Desiree Clary's rubies
Strangely enough Europe's most historic, if not richest, treasure trove of jewelry includes not a single ruby. And yet Jean-Baptiste Bernadotte's wife, the famous Desiree Clary, who at one time was engaged to Napoleon I, owned a set of matching diamond and ruby jewelry with an intricate foliate motif. This parure comprised a diadem, a necklace, a pair of girandole earrings and a brooch, and was given to her by her ex-fiance. They were the work of a Parisian jeweler whose name history, sadly, had forgotten but whose talent enabled him to create jewelry that was fit for a Queen despite the small size of the precious stones. Rather than surrounding a single ruby with small diamonds, as is usually the case, the skilful jeweler grouped together four and sometimes five small rubies in a gold prong setting in such a way to create the illusion of a single larger stone, sometimes measuring half to almost an inch across. Even the girandole earrings with their multiple decorative motifs, a classic in eighteenth century jewelry, were made using a similar technique to create the illusion that each pendant was a large pear-shaped ruby surrounded by diamonds.'
