Previously I said Cullinans I and II could be removed from the sceptre and Imperial State Crown on request.
Here is Queen Mary dressed for a Drawing Room when guests were presented at Buckingham Palace.
Queen Mary is wearing Cullinans I and II as a brooch. III is pendant to her diamond rivière and IV is on the band of Queen Victoria's Regal Circlet. The Koh-i-nûr is on the central element of the circlet. Queen Mary's own crown had not yet been altered for the arches to be removable.