Tiffany & Co. Eternity Diamond Wedding Band in 18kTiffany Co. Eternity Diamond Wedding Band in 18k. This iconic Schlumberger design for Tiffany Co. features 1. 76 carats of round brilliant cut diamonds set in platinum and 18 karat yellow gold. The sixteen (16) F color diamonds are separated into groups of two by the prominent yellow gold Xs. There is dramatic contrast of color as well as contrast of design elements in this brilliant piece of jewelry.