Some stones hold more than light.

A deep-blue diamond with a journey from India to the French royal collection and, eventually, the Smithsonian. A larger predecessor became the French Blue; after the theft of the French Crown Jewels in 1792, a smaller blue diamond appeared in London in 1812. It would take the Hope name from collector Henry Philip Hope.

Harry Winston, Inc. donated the gem to the Smithsonian in 1958. Its arrival was remarkably ordinary for such an extraordinary object: it travelled by registered mail in a plain package.

Look beyond the celebrity and notice its deep body colour. This is a very different way to appreciate diamond from searching for the most colourless stone. The Smithsonian also documents its red phosphorescence, another reminder that a gem’s response to light can be part of its scientific character.

The large red jewel in the front cross of Britain’s Imperial State Crown is a spinel. Its familiar name survives from a time when similar-looking red gems were not always distinguished by their mineral identity.

Historic Royal Palaces relates the tradition that Pedro of Castile gave it to Edward, the Black Prince, in 1367 after a military victory. Stories also place it in Henry V’s helmet at Agincourt. These early associations are presented as tradition and legend, rather than an unbroken modern ownership record.

The jewel’s identity makes its story more interesting. An exceptional red stone can earn its place in history on its own merits, even when the name attached to it turns out to be wrong.

At 423 carats, the Logan Sapphire is an extraordinary example of Sri Lankan sapphire. Its mixed cushion cut shows blue with a slight violet influence, framed by twenty diamonds in a silver and gold brooch.

Rebecca Pollard Guggenheim gave it to the Smithsonian in 1960, although she retained possession until 1971. By then she had married John A. Logan, giving the gem the name by which it is known today.

The museum records a June 1997 GIA report finding natural colour with no evidence of heat treatment. Here, size, colour, a documented treatment finding and a traceable modern history all add to the interest. Its scale is exceptional; the habit of looking closely at both stone and paperwork applies to a much smaller gem too.