I was unable to watch the State Opening of Parliament on television asI had planned, so I have been dependent of still images of its ceremonial. As I understand it the ceremony as it is today is essentially as codified in the reign of King Henry VIII, though clearly much of the ceremonial is considerably more ancient, and with later accretions - such as judicial wigs and with uniforms taking their design from the early nineteenth century.
It was King Henry VIII who observed that "We are at no time so high in our estate royal as in time of Parliament." Although he is a monarch with whom I would not always agree - and it is a safe enough distance in time to admit to disagreeing with him - in this case he was, barring the Coronation itself, right.
I did not realise until I read David Starkey's Monarchy that it has only been since 1913 that the Sovereign, once they have been crowned, has consistently worn the Imperial State Crown at the State Opening. I think Queen Victoria did in the 1850s, but in her widowhood on the few occasions she opened Parliament in person wore her small dress crown, and the Imperial State Crown was carried before her. This appears to have been the practice under King Edward VII, and it was King George V who began the modern practice of wearing the Crown to deliver the Gracious Speech. This would appear to have been part of thta process of enhancing the ceremonial surrounding the monarchy that began under his father, but which developed after 1910 with the revived Welsh Investiture and the presence of the King-Emperor at his Indian Durbar, complete with crown following on from the 1911 Coronation. Starkey says that the King found the crown uncomfortable and at various times during his reign adjustments were made to it to make it easier to wear.
The Imperial State Crown was remade for the present Queen, reverting to its original 1838 design with lower arches - they had been raised in the 1870s. I have seen a story of an ADC remembering seeing the Queen wearing the crown whilst eating her breakfast on the day of the State Opening so as to get used to balancing its three and a half pound weight on her head.
This view shows the back of the Imperial State Crown, and in particular the so-called Stuart sapphire in the circlet. This is said to have been confiscated by King Edward IV from Warwick the Kingmaker's brother Archbishop George Neville of York in the 1470s - it had decorated the archiepiscopal mitre - and to have been taken by King James II and VII in his pocket with him into exile in 1688. Bequeathed by his grandson Cardinal York (de jure King Henry IX) to King George III in 1807 it was set in the new crown in 1838 under the Black Prince's ruby in the front of the circlet, but was moved at King Edward VII's request to its present position to accommodate the second part of the Cullinan diamond in 1907.