The Diamond Diadem, which appears on stamps and currency and which is worn by the Queen on her way to and from the Opening of Parliament every year, was created by Rundells, the royal jeweler, for the Coronation of King George IV in 1820. The king probably wore it around his hat on the way to his coronation.

http://www.royalcollection.org.uk/eGallery/object.asp?object=31702&row=0&detail=feature

http://www.royalcollection.org.uk/eGallery/object.asp?object=31702&row=0&detail=about

Since then, the Diadem has been worn by queens, starting with Queen Adelaide. It has been pictured on every queen, starting with Queen Victoria, except apparently Queen Elizabeth (later the Queen Mother). But I am wondering how many queens have worn it to their coronations.

This is a set of pictures from my own files. I'm sorry, I don't know where I got them. They show the Diadem, two portraits of Queen Victoria wearing it, Queen Alexandra in her Coronation attire wearing first the Diadem and then her crown, two pictures of Queen Mary in I think two different gowns, Queen Elizabeth II wearing the Diadem at the beginning of her Coronation ceremony. The last two pictures do NOT show the Diadem; Queen Elizabeth (QM) and Queen Mary wore their own crowns without the arches to the Coronations of their children in 1937 and 1953. These two pictures also show that Queen Elizabeth, as she noted in her letters, wore Queen Mary's robe.

Edit: I have added to the set a third picture of Queen Alexandra, with the King, which may be a photo of them on the way to their coronation.

http://www.flickr.com/photos/digitaluser/sets/72157632479634737

I am wondering how many queens have worn the Diamond Diadem to their Coronations. Was it traditionally a coronation diadem, or was it probably worn only by King George IV, maybe Queen Alexandra, and Queen Elizabeth II as they traveled to and into Westminster Abbey?