Gatsby Jewellery Ltd has dated this piece to the 1910s.
The long bar part of the brooch is set with 22 (11 each side) rose cut diamonds of subtly graduating sizes. The platinum pin to the reverse is secured with a trombone clasp.

Accompanied by a report from The Gem & Pearl Laboratory (London) stating the pearls are natural, saltwater.
Cut – Rose cut diamonds.
Colour – The diamonds are H to I.
Clarity – The diamond are VS2 to SI2; all are clean to the naked eye.
Carat – A total approximate diamond weight of 0.47 carat
Circa – 1910.
Measurements – The brooch is 75.85mm long.
Weight – 6.6 grams
Metal – Platinum. Tested.
Gatsby Jewellery Ltd has dated this piece to the 1910s.
Gatsby jewellery are a husband and wife team who have years of knowledge and experience in dealing in fine antique jewellery.
You can view the stock and full dealer information on the Gatsby Jewellery Ltd Profile Page