Today is the centenary of the coronation of King George V and Queen Mary in 1911. There is an article with links about it here.
Amongsty other points of interest is the fact that this was the first British coronation ceremony, as opposed to the procession, to be recorded by photographs. This photograph shows the beginning of the ceremony in Westminster abbey.
It was King George who resumed the practice of being crowned with St Edward's Crown, rather than the lighter Imperial State Crown used by Queen Victoria and King Edward VII, although he quicly exchanged it for the Imperal crown. In 1937 and 1953 the monarch was to wear St Edward's Crown right up to the communion, only assuming the Imperial Stae Crown at the Recess for the procession out of the abbey and back to the palace. It was the King who ordered that St Edwar's Crown be permanently set with precious and semi-precious stones, rather than the previous practice of hiring gems for the Coronation and then replacing them with paste.
It was only fairly recently that I discovered that it was King George V who from the 1913 State Opening of Parliament actually wore the Imperial State Crown with his robes of state, and this has remained the practice. at Queen Victoria's few post 1861 State Openings and those of King Edward VII the crown was carried on its cushion, although the Sovereign wore the robes.
St Edward's Crown
The 1911 Coronation was, I think, the only time that Queen Mary's crown was used with its arches. Like Queen Alexandra's 1902 crown, but unlike those of 1831 for Queen Adelaide and 1937 for Queen Elizabeth, it has eight half arches rather than the more traditional four. In design it is very like the Crown of India, which was also made by Garrards that year - but I will say more about that in December.
Queen Mary's Crown
The crown contains some 2,200 diamonds and in 1911 it contained the Koh-i-Noor diamond as well as Cullinan III and Cullinan IV (the Cullinan diamond had been presented to King Edward VII and after cutting the largest piece was set in the sceptre and the second largest in the Imperial Stae Crown, displacing to the back of the circlet the Stuart Sapphire). In 1914 they were replaced by crystal models.
Unlike many earlier coronation crowns, it was specially constructed so that its arches could be removed, allowing it to be worn as a circlet, and it was in that way that Queen Mary wore it for State Openings and at the Coronation of King George VI in 1937. At her funeral in 1953 I understand that her crown did not rest on her coffin, unlike the practice at the funeral of Queen Elizabeth in 2002.