Charles Arfvidson supplied Boucheron with similar blued steel jewels in the early 1900’s. A diamond and blue steel regency style necklace by Arfvidson is held in the Boucheron Collection.
See Boucheron: Four Generations of a World-Renowned Jeweler, Neret, Gilles, trans. Purcell,(NY, 1988), page 35.
The contrasting combination of black metal and diamonds is highly effective and much copied by modern jewellers.