So far the exact date of the original portrait used as the source for this miniature has not been identified. The pose is similar to, but not identical with, a portrait taken in 1886 and shown here, which was used on the cover of some sheet music published in 1886 to celebrate her 1887 Jubilee. However, a close up comparison shows she is younger than in the 1886 portrait.The Queen also looks somewhat younger than the 1887 and 1897 Jubilee portraits.
In the miniature she appears to be wearing the George IV Diadem Crown. In 1870, when she was 52 years old, the Queen had asked for a small state crown to be made as the previous state one was too heavy. This was the Queen Victoria Small Crown and she then wore it for all state occasions from the date of the state opening of Parliament on 9 Feb 1871.
Thus after 1870, it seems Queen Victoria did not normally wear the George IV Diadem Crown for formal portraits, although she is wearing it here.
Queen Elizabeth now wears the George IV Diadem crown, although the design is not identical to that worn by Queen Victoria, as it was apparently reset in 1902 for Queen Alexandria. 1208