A Ring gold set with calibrated rubies and 1 Lisbon cut diamond with an approximate weight of 2.93 ct., colour degree K and clarity SI2, medium fluorescence Portuguese 20th C. (mid) ring with signs of use and minor defects without mark, pursuant to Decreto-Lei 120/2017 of 15 September - art. 2nd, paragraph 2, point (c) Dimensões (altura x comprimento x largura) - 16 (17,7 mm) cm; Peso - 3,5 g. Notes: Provenance: Jewelry Collection of a Soprano of the São Carlos National Opera House, Lisbon.

Note: The originality and the rarity of the cut of this diamond imposes an explanation to underline the cultural and patrimonial reach, on a national and international level, of this stone.
At first sight cut as a brilliant, a designation reserved for a cut showing a total of 58 facets, being 33 in the top section and 25 in the bottom section, this diamond, which is presented carved in  a later gold ring, reproduced ahead, decorated with rubies, shows in fact 41 facets in the top section (known as the crown), which corresponds to the Lisbon Cut.
Though mentioned in the professional litterature at least since mid 19th C., according to the Gemmologist Rui Galopim de Carvalho, in The Journal of Gemmology 34(2) 2014, to this day, the Lisbon Cut has been found, by himself, in no more than one diamond: one of the biggest diamonds decorating the famous snuff box commissioned in 1755 by King D. José I of Portugal to the French orfèvre Jacqmin (1718-1770) and executed in 1755/1756 by the French jeweler Jean Ducrollay.
On the mentioned snuff box, decorated with 204 emeralds and 853 Brilliant Cut diamonds, one of them, with an approximate weight of 10 ct, located on the cover, close to the lock, boasts the Lisbon Cut on his crown: 41 facets; and 25 on the bottom.
This is the second diamond showing such a Cut.  
The systematic and careful analyses of the jewellery, namely stones, undertaken by our experts during the process that preceds the contract, the insertion in the catalogue and the correspondente sale, revealed that the crown of this diamond has in fact the 41 facets that define the Lisbon Cut and that distinguish it from the classic Brilliant Cut; once removed from the ring it was possible to analyse the bottom section and the result was that, as occurs with the diamond decorating the snuff box, it has no more than 25 facets.   
Being known, or being known to our experts the existence of only two diamonds with such a Cut – with 41 facets on the crown, 8 more than the Brilliant Cut – it is clear the rarity of this diamond.
On the other hand, having both two diamonds a bottom section  with no more than 25 facets, that fact may lead to the conclusion that thew Lisbon Cut has in fact but 8 extra facets on the top section, contrary to what was believed.
The future – and the possible appearence in the market of another diamond with the Lisbon Cut – will allow to confirm (or not) that presumption.
For the moment, we would like to congratulate our Silver and Jewels experts, particularly Henrique Correia Braga, for his lynx eyes that allow him to discover this diamond; and for his extensive knowledge  that allow him the correct identification and the revelation of its rare, precious cut – that few would know or recognise, among so many others, as he did. We thank him also for his research work: this note is based on it.
February 2020
The Managins Partners