From the current royal families the most valuable diadem must be the one from the so-called "New Crown Parure" in the House of Orange-Nassau (the Netherlands). (
picture).
The sheer size of the diamonds, their carat power and their purest clarity are the summum of what one can wish for. The diadem also contains diamonds unbroken in possession of same royal family. For an example the biggest diamond topping this diadem was purchased in 1690 (!) by Willem III of Nassau, Prince of Orange for his spouse Mary II Stuart. Not only is it a large diamond, it is also a pale blue color with a greenish sea tint - a combination which makes this an incredibly rare and valuable stone.
Other big diadems like the Empire Diadem (
picture) in the Nassau-collection (Luxembourg) and the Brazilean Diadem (
picture) in the Bernadotte collection are BIG too but miss the eyepopping diamond powerguns and are also not that long in the collection. The value of the blue diamond topping the Dutch one can exceed the whole value of the Brazilean Diadem.
The size of the Luxembourgean and Swedish diadems are mind-boggling. A closer look learns that these diadems have a lot of filigrain scrollwork set with small diamonds en-pavé, filling the monture. The biggest single diamonds in both diadems are smaller than the main stones in the monture of the Dutch diadem. The bigger diamonds in the Luxembourgian Empire Diadem have a yellowish colour. Back then it was a cheaper than diamonds of pure clarity. So in carat-power and in the sheer size of stones it logs a bit behind. The effect however remains eye-popping and that is exactly why these diadems were made for, of course,
